129 ideas
| 7001 | If you begin philosophy with language, you find yourself trapped in it [Heil] |
| Full Idea: If you start with language and try to work your way outwards, you will never get outside language. | |
| From: John Heil (From an Ontological Point of View [2003], Pref) | |
| A reaction: This voices my pessimism about the linguistic approach to philosophy (and I don't just mean analysis of ordinary language), though I wonder if the career of (say) John Searle is a counterexample. |
| 7038 | A theory with few fundamental principles might still posit a lot of entities [Heil] |
| Full Idea: It could well turn out that a simpler theory - a theory with fewer fundamental principles - posits more entities than a more complex competitor. | |
| From: John Heil (From an Ontological Point of View [2003], 13.6) | |
| A reaction: See also Idea 4036. The point here is that you can't simply translate Ockham as 'keep it simple', as there are different types of simplicity. The best theory will negotiate a balance between entities and principles. |
| 7037 | Parsimony does not imply the world is simple, but that our theories should try to be [Heil] |
| Full Idea: A commitment to parsimony is not a commitment to a conception of the world as simple. The idea, rather, is that we should not complicate our theories about the world unnecessarily. | |
| From: John Heil (From an Ontological Point of View [2003], 13.6) | |
| A reaction: In other words, Ockham's Razor is about us, not about the world. It would be absurd to make the a priori assumption that the world has to be simple. Are we, though, creating bad theories by insisting that they should be simple? |
| 7004 | The view that truth making is entailment is misguided and misleading [Heil] |
| Full Idea: I argue that the widely held view that truth making is to be understood as entailment is misguided in principle and potentially misleading. | |
| From: John Heil (From an Ontological Point of View [2003], Intro) | |
| A reaction: If reality was just one particle, what would entail the truths about it? Suppose something appears to be self-evident true about reality, but no one can think of any entailments to derive it? Do we assume a priori that they are possible? |
| 13439 | Venn Diagrams map three predicates into eight compartments, then look for the conclusion [Bostock] |
| Full Idea: Venn Diagrams are a traditional method to test validity of syllogisms. There are three interlocking circles, one for each predicate, thus dividing the universe into eight possible basic elementary quantifications. Is the conclusion in a compartment? | |
| From: David Bostock (Intermediate Logic [1997], 3.8) |
| 13421 | 'Disjunctive Normal Form' is ensuring that no conjunction has a disjunction within its scope [Bostock] |
| Full Idea: 'Disjunctive Normal Form' (DNF) is rearranging the occurrences of ∧ and ∨ so that no conjunction sign has any disjunction in its scope. This is achieved by applying two of the distribution laws. | |
| From: David Bostock (Intermediate Logic [1997], 2.6) |
| 13422 | 'Conjunctive Normal Form' is ensuring that no disjunction has a conjunction within its scope [Bostock] |
| Full Idea: 'Conjunctive Normal Form' (CNF) is rearranging the occurrences of ∧ and ∨ so that no disjunction sign has any conjunction in its scope. This is achieved by applying two of the distribution laws. | |
| From: David Bostock (Intermediate Logic [1997], 2.6) |
| 13355 | 'Disjunction' says that Γ,φ∨ψ|= iff Γ,φ|= and Γ,ψ|= [Bostock] |
| Full Idea: The Principle of Disjunction says that Γ,φ∨ψ |= iff Γ,φ |= and Γ,ψ |=. | |
| From: David Bostock (Intermediate Logic [1997], 2.5.G) | |
| A reaction: That is, a disjunction leads to a contradiction if they each separately lead to contradictions. |
| 13350 | 'Assumptions' says that a formula entails itself (φ|=φ) [Bostock] |
| Full Idea: The Principle of Assumptions says that any formula entails itself, i.e. φ |= φ. The principle depends just upon the fact that no interpretation assigns both T and F to the same formula. | |
| From: David Bostock (Intermediate Logic [1997], 2.5.A) | |
| A reaction: Thus one can introduce φ |= φ into any proof, and then use it to build more complex sequents needed to attain a particular target formula. Bostock's principle is more general than anything in Lemmon. |
| 13351 | 'Thinning' allows that if premisses entail a conclusion, then adding further premisses makes no difference [Bostock] |
| Full Idea: The Principle of Thinning says that if a set of premisses entails a conclusion, then adding further premisses will still entail the conclusion. It is 'thinning' because it makes a weaker claim. If γ|=φ then γ,ψ|= φ. | |
| From: David Bostock (Intermediate Logic [1997], 2.5.B) | |
| A reaction: It is also called 'premise-packing'. It is the characteristic of a 'monotonic' logic - where once something is proved, it stays proved, whatever else is introduced. |
| 13356 | The 'conditional' is that Γ|=φ→ψ iff Γ,φ|=ψ [Bostock] |
| Full Idea: The Conditional Principle says that Γ |= φ→ψ iff Γ,φ |= ψ. With the addition of negation, this implies φ,φ→ψ |= ψ, which is 'modus ponens'. | |
| From: David Bostock (Intermediate Logic [1997], 2.5.H) | |
| A reaction: [Second half is in Ex. 2.5.4] |
| 13352 | 'Cutting' allows that if x is proved, and adding y then proves z, you can go straight to z [Bostock] |
| Full Idea: The Principle of Cutting is the general point that entailment is transitive, extending this to cover entailments with more than one premiss. Thus if γ |= φ and φ,Δ |= ψ then γ,Δ |= ψ. Here φ has been 'cut out'. | |
| From: David Bostock (Intermediate Logic [1997], 2.5.C) | |
| A reaction: It might be called the Principle of Shortcutting, since you can get straight to the last conclusion, eliminating the intermediate step. |
| 13353 | 'Negation' says that Γ,¬φ|= iff Γ|=φ [Bostock] |
| Full Idea: The Principle of Negation says that Γ,¬φ |= iff Γ |= φ. We also say that φ,¬φ |=, and hence by 'thinning on the right' that φ,¬φ |= ψ, which is 'ex falso quodlibet'. | |
| From: David Bostock (Intermediate Logic [1997], 2.5.E) | |
| A reaction: That is, roughly, if the formula gives consistency, the negation gives contradiction. 'Ex falso' says that anything will follow from a contradiction. |
| 13354 | 'Conjunction' says that Γ|=φ∧ψ iff Γ|=φ and Γ|=ψ [Bostock] |
| Full Idea: The Principle of Conjunction says that Γ |= φ∧ψ iff Γ |= φ and Γ |= ψ. This implies φ,ψ |= φ∧ψ, which is ∧-introduction. It is also implies ∧-elimination. | |
| From: David Bostock (Intermediate Logic [1997], 2.5.F) | |
| A reaction: [Second half is Ex. 2.5.3] That is, if they are entailed separately, they are entailed as a unit. It is a moot point whether these principles are theorems of propositional logic, or derivation rules. |
| 13610 | A logic with ¬ and → needs three axiom-schemas and one rule as foundation [Bostock] |
| Full Idea: For ¬,→ Schemas: (A1) |-φ→(ψ→φ), (A2) |-(φ→(ψ→ξ)) → ((φ→ψ)→(φ→ξ)), (A3) |-(¬φ→¬ψ) → (ψ→φ), Rule:DET:|-φ,|-φ→ψ then |-ψ | |
| From: David Bostock (Intermediate Logic [1997], 5.2) | |
| A reaction: A1 says everything implies a truth, A2 is conditional proof, and A3 is contraposition. DET is modus ponens. This is Bostock's compact near-minimal axiom system for proposition logic. He adds two axioms and another rule for predicate logic. |
| 13846 | A 'free' logic can have empty names, and a 'universally free' logic can have empty domains [Bostock] |
| Full Idea: A 'free' logic is one in which names are permitted to be empty. A 'universally free' logic is one in which the domain of an interpretation may also be empty. | |
| From: David Bostock (Intermediate Logic [1997], 8.6) |
| 7035 | God does not create the world, and then add the classes [Heil] |
| Full Idea: It is hard to see classes as an 'addition of being'; God does not create the world, and then add the classes. | |
| From: John Heil (From an Ontological Point of View [2003], 13.4 n6) | |
| A reaction: This seems right. We may be tempted into believing in the reality of classes when considering maths, but it seems utterly implausible when considering trees or cows. |
| 13346 | Truth is the basic notion in classical logic [Bostock] |
| Full Idea: The most fundamental notion in classical logic is that of truth. | |
| From: David Bostock (Intermediate Logic [1997], 1.1) | |
| A reaction: The opening sentence of his book. Hence the first half of the book is about semantics, and only the second half deals with proof. Compare Idea 10282. The thought seems to be that you could leave out truth, but that makes logic pointless. |
| 13545 | Elementary logic cannot distinguish clearly between the finite and the infinite [Bostock] |
| Full Idea: In very general terms, we cannot express the distinction between what is finite and what is infinite without moving essentially beyond the resources available in elementary logic. | |
| From: David Bostock (Intermediate Logic [1997], 4.8) | |
| A reaction: This observation concludes a discussion of Compactness in logic. |
| 13822 | Fictional characters wreck elementary logic, as they have contradictions and no excluded middle [Bostock] |
| Full Idea: Discourse about fictional characters leads to a breakdown of elementary logic. We accept P or ¬P if the relevant story says so, but P∨¬P will not be true if the relevant story says nothing either way, and P∧¬P is true if the story is inconsistent. | |
| From: David Bostock (Intermediate Logic [1997], 8.5) | |
| A reaction: I really like this. Does one need to invent a completely new logic for fictional characters? Or must their logic be intuitionist, or paraconsistent, or both? |
| 13623 | The syntactic turnstile |- φ means 'there is a proof of φ' or 'φ is a theorem' [Bostock] |
| Full Idea: The syntactic turnstile |- φ means 'There is a proof of φ' (in the system currently being considered). Another way of saying the same thing is 'φ is a theorem'. | |
| From: David Bostock (Intermediate Logic [1997], 5.1) |
| 13347 | Validity is a conclusion following for premises, even if there is no proof [Bostock] |
| Full Idea: The classical definition of validity counts an argument as valid if and only if the conclusion does in fact follow from the premises, whether or not the argument contains any demonstration of this fact. | |
| From: David Bostock (Intermediate Logic [1997], 1.2) | |
| A reaction: Hence validity is given by |= rather than by |-. A common example is 'it is red so it is coloured', which seems true but beyond proof. In the absence of formal proof, you wonder whether validity is merely a psychological notion. |
| 13348 | It seems more natural to express |= as 'therefore', rather than 'entails' [Bostock] |
| Full Idea: In practice we avoid quotation marks and explicitly set-theoretic notation that explaining |= as 'entails' appears to demand. Hence it seems more natural to explain |= as simply representing the word 'therefore'. | |
| From: David Bostock (Intermediate Logic [1997], 1.3) | |
| A reaction: Not sure I quite understand that, but I have trained myself to say 'therefore' for the generic use of |=. In other consequences it seems better to read it as 'semantic consequence', to distinguish it from |-. |
| 13349 | Γ|=φ is 'entails'; Γ|= is 'is inconsistent'; |=φ is 'valid' [Bostock] |
| Full Idea: If we write Γ |= φ, with one formula to the right, then the turnstile abbreviates 'entails'. For a sequent of the form Γ |= it can be read as 'is inconsistent'. For |= φ we read it as 'valid'. | |
| From: David Bostock (Intermediate Logic [1997], 1.3) |
| 13614 | MPP: 'If Γ|=φ and Γ|=φ→ψ then Γ|=ψ' (omit Γs for Detachment) [Bostock] |
| Full Idea: The Rule of Detachment is a version of Modus Ponens, and says 'If |=φ and |=φ→ψ then |=ψ'. This has no assumptions. Modus Ponens is the more general rule that 'If Γ|=φ and Γ|=φ→ψ then Γ|=ψ'. | |
| From: David Bostock (Intermediate Logic [1997], 5.3) | |
| A reaction: Modus Ponens is actually designed for use in proof based on assumptions (which isn't always the case). In Detachment the formulae are just valid, without dependence on assumptions to support them. |
| 13617 | MPP is a converse of Deduction: If Γ |- φ→ψ then Γ,φ|-ψ [Bostock] |
| Full Idea: Modus Ponens is equivalent to the converse of the Deduction Theorem, namely 'If Γ |- φ→ψ then Γ,φ|-ψ'. | |
| From: David Bostock (Intermediate Logic [1997], 5.3) | |
| A reaction: See 13615 for details of the Deduction Theorem. See 13614 for Modus Ponens. |
| 13799 | The sign '=' is a two-place predicate expressing that 'a is the same thing as b' (a=b) [Bostock] |
| Full Idea: We shall use 'a=b' as short for 'a is the same thing as b'. The sign '=' thus expresses a particular two-place predicate. Officially we will use 'I' as the identity predicate, so that 'Iab' is as formula, but we normally 'abbreviate' this to 'a=b'. | |
| From: David Bostock (Intermediate Logic [1997], 8.1) |
| 13800 | |= α=α and α=β |= φ(α/ξ ↔ φ(β/ξ) fix identity [Bostock] |
| Full Idea: We usually take these two principles together as the basic principles of identity: |= α=α and α=β |= φ(α/ξ) ↔ φ(β/ξ). The second (with scant regard for history) is known as Leibniz's Law. | |
| From: David Bostock (Intermediate Logic [1997], 8.1) |
| 13803 | If we are to express that there at least two things, we need identity [Bostock] |
| Full Idea: To say that there is at least one thing x such that Fx we need only use an existential quantifier, but to say that there are at least two things we need identity as well. | |
| From: David Bostock (Intermediate Logic [1997], 8.1) | |
| A reaction: The only clear account I've found of why logic may need to be 'with identity'. Without it, you can only reason about one thing or all things. Presumably plural quantification no longer requires '='? |
| 13357 | Truth-functors are usually held to be defined by their truth-tables [Bostock] |
| Full Idea: The usual view of the meaning of truth-functors is that each is defined by its own truth-table, independently of any other truth-functor. | |
| From: David Bostock (Intermediate Logic [1997], 2.7) |
| 13812 | A 'zero-place' function just has a single value, so it is a name [Bostock] |
| Full Idea: We can talk of a 'zero-place' function, which is a new-fangled name for a familiar item; it just has a single value, and so it has the same role as a name. | |
| From: David Bostock (Intermediate Logic [1997], 8.2) |
| 13811 | A 'total' function ranges over the whole domain, a 'partial' function over appropriate inputs [Bostock] |
| Full Idea: Usually we allow that a function is defined for arguments of a suitable kind (a 'partial' function), but we can say that each function has one value for any object whatever, from the whole domain that our quantifiers range over (a 'total' function). | |
| From: David Bostock (Intermediate Logic [1997], 8.2) | |
| A reaction: He points out (p.338) that 'the father of..' is a functional expression, but it wouldn't normally take stones as input, so seems to be a partial function. But then it doesn't even take all male humans either. It only takes fathers! |
| 13360 | In logic, a name is just any expression which refers to a particular single object [Bostock] |
| Full Idea: The important thing about a name, for logical purposes, is that it is used to make a singular reference to a particular object; ..we say that any expression too may be counted as a name, for our purposes, it it too performs the same job. | |
| From: David Bostock (Intermediate Logic [1997], 3.1) | |
| A reaction: He cites definite descriptions as the most notoriously difficult case, in deciding whether or not they function as names. I takes it as pretty obvious that sometimes they do and sometimes they don't (in ordinary usage). |
| 13361 | An expression is only a name if it succeeds in referring to a real object [Bostock] |
| Full Idea: An expression is not counted as a name unless it succeeds in referring to an object, i.e. unless there really is an object to which it refers. | |
| From: David Bostock (Intermediate Logic [1997], 3.1) | |
| A reaction: His 'i.e.' makes the existence condition sound sufficient, but in ordinary language you don't succeed in referring to 'that man over there' just because he exists. In modal contexts we presumably refer to hypothetical objects (pace Lewis). |
| 13813 | Definite descriptions don't always pick out one thing, as in denials of existence, or errors [Bostock] |
| Full Idea: It is natural to suppose one only uses a definite description when one believes it describes only one thing, but exceptions are 'there is no such thing as the greatest prime number', or saying something false where the reference doesn't occur. | |
| From: David Bostock (Intermediate Logic [1997], 8.3) |
| 13814 | Definite desciptions resemble names, but can't actually be names, if they don't always refer [Bostock] |
| Full Idea: Although a definite description looks like a complex name, and in many ways behaves like a name, still it cannot be a name if names must always refer to objects. Russell gave the first proposal for handling such expressions. | |
| From: David Bostock (Intermediate Logic [1997], 8.3) | |
| A reaction: I take the simple solution to be a pragmatic one, as roughly shown by Donnellan, that sometimes they are used exactly like names, and sometimes as something else. The same phrase can have both roles. Confusing for logicians. Tough. |
| 13816 | Because of scope problems, definite descriptions are best treated as quantifiers [Bostock] |
| Full Idea: Because of the scope problem, it now seems better to 'parse' definition descriptions not as names but as quantifiers. 'The' is to be treated in the same category as acknowledged quantifiers like 'all' and 'some'. We write Ix - 'for the x such that..'. | |
| From: David Bostock (Intermediate Logic [1997], 8.3) | |
| A reaction: This seems intuitively rather good, since quantification in normal speech is much more sophisticated than the crude quantification of classical logic. But the fact is that they often function as names (but see Idea 13817). |
| 13817 | Definite descriptions are usually treated like names, and are just like them if they uniquely refer [Bostock] |
| Full Idea: In practice, definite descriptions are for the most part treated as names, since this is by far the most convenient notation (even though they have scope). ..When a description is uniquely satisfied then it does behave like a name. | |
| From: David Bostock (Intermediate Logic [1997], 8.3) | |
| A reaction: Apparent names themselves have problems when they wander away from uniquely picking out one thing, as in 'John Doe'. |
| 13848 | We are only obliged to treat definite descriptions as non-names if only the former have scope [Bostock] |
| Full Idea: If it is really true that definite descriptions have scopes whereas names do not, then Russell must be right to claim that definite descriptions are not names. If, however, this is not true, then it does no harm to treat descriptions as complex names. | |
| From: David Bostock (Intermediate Logic [1997], 8.8) |
| 13815 | Names do not have scope problems (e.g. in placing negation), but Russell's account does have that problem [Bostock] |
| Full Idea: In orthodox logic names are not regarded as having scope (for example, in where a negation is placed), whereas on Russell's theory definite descriptions certainly do. Russell had his own way of dealing with this. | |
| From: David Bostock (Intermediate Logic [1997], 8.3) |
| 13438 | 'Prenex normal form' is all quantifiers at the beginning, out of the scope of truth-functors [Bostock] |
| Full Idea: A formula is said to be in 'prenex normal form' (PNF) iff all its quantifiers occur in a block at the beginning, so that no quantifier is in the scope of any truth-functor. | |
| From: David Bostock (Intermediate Logic [1997], 3.7) | |
| A reaction: Bostock provides six equivalences which can be applied to manouevre any formula into prenex normal form. He proves that every formula can be arranged in PNF. |
| 13818 | If we allow empty domains, we must allow empty names [Bostock] |
| Full Idea: We can show that if empty domains are permitted, then empty names must be permitted too. | |
| From: David Bostock (Intermediate Logic [1997], 8.4) |
| 13801 | An 'informal proof' is in no particular system, and uses obvious steps and some ordinary English [Bostock] |
| Full Idea: An 'informal proof' is not in any particular proof system. One may use any rule of proof that is 'sufficiently obvious', and there is quite a lot of ordinary English in the proof, explaining what is going on at each step. | |
| From: David Bostock (Intermediate Logic [1997], 8.1) |
| 13619 | Quantification adds two axiom-schemas and a new rule [Bostock] |
| Full Idea: New axiom-schemas for quantifiers: (A4) |-∀ξφ → φ(α/ξ), (A5) |-∀ξ(ψ→φ) → (ψ→∀ξφ), plus the rule GEN: If |-φ the |-∀ξφ(ξ/α). | |
| From: David Bostock (Intermediate Logic [1997], 5.6) | |
| A reaction: This follows on from Idea 13610, where he laid out his three axioms and one rule for propositional (truth-functional) logic. This Idea plus 13610 make Bostock's proposed axiomatisation of first-order logic. |
| 13622 | Axiom systems from Frege, Russell, Church, Lukasiewicz, Tarski, Nicod, Kleene, Quine... [Bostock] |
| Full Idea: Notably axiomatisations of first-order logic are by Frege (1879), Russell and Whitehead (1910), Church (1956), Lukasiewicz and Tarski (1930), Lukasiewicz (1936), Nicod (1917), Kleene (1952) and Quine (1951). Also Bostock (1997). | |
| From: David Bostock (Intermediate Logic [1997], 5.8) | |
| A reaction: My summary, from Bostock's appendix 5.8, which gives details of all of these nine systems. This nicely illustrates the status and nature of axiom systems, which have lost the absolute status they seemed to have in Euclid. |
| 13615 | 'Conditonalised' inferences point to the Deduction Theorem: If Γ,φ|-ψ then Γ|-φ→ψ [Bostock] |
| Full Idea: If a group of formulae prove a conclusion, we can 'conditionalize' this into a chain of separate inferences, which leads to the Deduction Theorem (or Conditional Proof), that 'If Γ,φ|-ψ then Γ|-φ→ψ'. | |
| From: David Bostock (Intermediate Logic [1997], 5.3) | |
| A reaction: This is the rule CP (Conditional Proof) which can be found in the rules for propositional logic I transcribed from Lemmon's book. |
| 13616 | The Deduction Theorem greatly simplifies the search for proof [Bostock] |
| Full Idea: Use of the Deduction Theorem greatly simplifies the search for proof (or more strictly, the task of showing that there is a proof). | |
| From: David Bostock (Intermediate Logic [1997], 5.3) | |
| A reaction: See 13615 for details of the Deduction Theorem. Bostock is referring to axiomatic proof, where it can be quite hard to decide which axioms are relevant. The Deduction Theorem enables the making of assumptions. |
| 13620 | Proof by Assumptions can always be reduced to Proof by Axioms, using the Deduction Theorem [Bostock] |
| Full Idea: By repeated transformations using the Deduction Theorem, any proof from assumptions can be transformed into a fully conditionalized proof, which is then an axiomatic proof. | |
| From: David Bostock (Intermediate Logic [1997], 5.6) | |
| A reaction: Since proof using assumptions is perhaps the most standard proof system (e.g. used in Lemmon, for many years the standard book at Oxford University), the Deduction Theorem is crucial for giving it solid foundations. |
| 13621 | The Deduction Theorem and Reductio can 'discharge' assumptions - they aren't needed for the new truth [Bostock] |
| Full Idea: Like the Deduction Theorem, one form of Reductio ad Absurdum (If Γ,φ|-[absurdity] then Γ|-¬φ) 'discharges' an assumption. Assume φ and obtain a contradiction, then we know ¬&phi, without assuming φ. | |
| From: David Bostock (Intermediate Logic [1997], 5.7) | |
| A reaction: Thus proofs from assumption either arrive at conditional truths, or at truths that are true irrespective of what was initially assumed. |
| 13753 | Natural deduction takes proof from assumptions (with its rules) as basic, and axioms play no part [Bostock] |
| Full Idea: Natural deduction takes the notion of proof from assumptions as a basic notion, ...so it will use rules for use in proofs from assumptions, and axioms (as traditionally understood) will have no role to play. | |
| From: David Bostock (Intermediate Logic [1997], 6.1) | |
| A reaction: The main rules are those for introduction and elimination of truth functors. |
| 13755 | Excluded middle is an introduction rule for negation, and ex falso quodlibet will eliminate it [Bostock] |
| Full Idea: Many books take RAA (reductio) and DNE (double neg) as the natural deduction introduction- and elimination-rules for negation, but RAA is not a natural introduction rule. I prefer TND (tertium) and EFQ (ex falso) for ¬-introduction and -elimination. | |
| From: David Bostock (Intermediate Logic [1997], 6.2) |
| 13758 | In natural deduction we work from the premisses and the conclusion, hoping to meet in the middle [Bostock] |
| Full Idea: When looking for a proof of a sequent, the best we can do in natural deduction is to work simultaneously in both directions, forward from the premisses, and back from the conclusion, and hope they will meet in the middle. | |
| From: David Bostock (Intermediate Logic [1997], 6.5) |
| 13754 | Natural deduction rules for → are the Deduction Theorem (→I) and Modus Ponens (→E) [Bostock] |
| Full Idea: Natural deduction adopts for → as rules the Deduction Theorem and Modus Ponens, here called →I and →E. If ψ follows φ in the proof, we can write φ→ψ (→I). φ and φ→ψ permit ψ (→E). | |
| From: David Bostock (Intermediate Logic [1997], 6.2) | |
| A reaction: Natural deduction has this neat and appealing way of formally introducing or eliminating each connective, so that you know where you are, and you know what each one means. |
| 13611 | Tableau proofs use reduction - seeking an impossible consequence from an assumption [Bostock] |
| Full Idea: A tableau proof is a proof by reduction ad absurdum. One begins with an assumption, and one develops the consequences of that assumption, seeking to derive an impossible consequence. | |
| From: David Bostock (Intermediate Logic [1997], 4.1) |
| 13613 | A completed open branch gives an interpretation which verifies those formulae [Bostock] |
| Full Idea: An open branch in a completed tableau will always yield an interpretation that verifies every formula on the branch. | |
| From: David Bostock (Intermediate Logic [1997], 4.7) | |
| A reaction: In other words the open branch shows a model which seems to work (on the available information). Similarly a closed branch gives a model which won't work - a counterexample. |
| 13612 | Non-branching rules add lines, and branching rules need a split; a branch with a contradiction is 'closed' [Bostock] |
| Full Idea: Rules for semantic tableaus are of two kinds - non-branching rules and branching rules. The first allow the addition of further lines, and the second requires splitting the branch. A branch which assigns contradictory values to a formula is 'closed'. | |
| From: David Bostock (Intermediate Logic [1997], 4.1) | |
| A reaction: [compressed] Thus 'and' stays on one branch, asserting both formulae, but 'or' splits, checking first one and then the other. A proof succeeds when all the branches are closed, showing that the initial assumption leads only to contradictions. |
| 13761 | In a tableau proof no sequence is established until the final branch is closed; hypotheses are explored [Bostock] |
| Full Idea: In a tableau system no sequent is established until the final step of the proof, when the last branch closes, and until then we are simply exploring a hypothesis. | |
| From: David Bostock (Intermediate Logic [1997], 7.3) | |
| A reaction: This compares sharply with a sequence calculus, where every single step is a conclusive proof of something. So use tableaux for exploring proofs, and then sequence calculi for writing them up? |
| 13756 | A tree proof becomes too broad if its only rule is Modus Ponens [Bostock] |
| Full Idea: When the only rule of inference is Modus Ponens, the branches of a tree proof soon spread too wide for comfort. | |
| From: David Bostock (Intermediate Logic [1997], 6.4) |
| 13762 | Tableau rules are all elimination rules, gradually shortening formulae [Bostock] |
| Full Idea: In their original setting, all the tableau rules are elimination rules, allowing us to replace a longer formula by its shorter components. | |
| From: David Bostock (Intermediate Logic [1997], 7.3) |
| 13757 | Unlike natural deduction, semantic tableaux have recipes for proving things [Bostock] |
| Full Idea: With semantic tableaux there are recipes for proof-construction that we can operate, whereas with natural deduction there are not. | |
| From: David Bostock (Intermediate Logic [1997], 6.5) |
| 13760 | A sequent calculus is good for comparing proof systems [Bostock] |
| Full Idea: A sequent calculus is a useful tool for comparing two systems that at first look utterly different (such as natural deduction and semantic tableaux). | |
| From: David Bostock (Intermediate Logic [1997], 7.2) |
| 13759 | Each line of a sequent calculus is a conclusion of previous lines, each one explicitly recorded [Bostock] |
| Full Idea: A sequent calculus keeps an explicit record of just what sequent is established at each point in a proof. Every line is itself the sequent proved at that point. It is not a linear sequence or array of formulae, but a matching array of whole sequents. | |
| From: David Bostock (Intermediate Logic [1997], 7.1) |
| 13364 | Interpretation by assigning objects to names, or assigning them to variables first [Bostock, by PG] |
| Full Idea: There are two approaches to an 'interpretation' of a logic: the first method assigns objects to names, and then defines connectives and quantifiers, focusing on truth; the second assigns objects to variables, then variables to names, using satisfaction. | |
| From: report of David Bostock (Intermediate Logic [1997], 3.4) by PG - Db (lexicon) | |
| A reaction: [a summary of nine elusive pages in Bostock] He says he prefers the first method, but the second method is more popular because it handles open formulas, by treating free variables as if they were names. |
| 13821 | Extensionality is built into ordinary logic semantics; names have objects, predicates have sets of objects [Bostock] |
| Full Idea: Extensionality is built into the semantics of ordinary logic. When a name-letter is interpreted as denoting something, we just provide the object denoted. All that we provide for a one-place predicate-letter is the set of objects that it is true of.. | |
| From: David Bostock (Intermediate Logic [1997]) | |
| A reaction: Could we keep the syntax of ordinary logic, and provide a wildly different semantics, much closer to real life? We could give up these dreadful 'objects' that Frege lumbered us with. Logic for processes, etc. |
| 13362 | If an object has two names, truth is undisturbed if the names are swapped; this is Extensionality [Bostock] |
| Full Idea: If two names refer to the same object, then in any proposition which contains either of them the other may be substituted in its place, and the truth-value of the proposition of the proposition will be unaltered. This is the Principle of Extensionality. | |
| From: David Bostock (Intermediate Logic [1997], 3.1) | |
| A reaction: He acknowledges that ordinary language is full of counterexamples, such as 'he doesn't know the Morning Star and the Evening Star are the same body' (when he presumably knows that the Morning Star is the Morning Star). This is logic. Like maths. |
| 13541 | For 'negation-consistent', there is never |-(S)φ and |-(S)¬φ [Bostock] |
| Full Idea: Any system of proof S is said to be 'negation-consistent' iff there is no formula such that |-(S)φ and |-(S)¬φ. | |
| From: David Bostock (Intermediate Logic [1997], 4.5) | |
| A reaction: Compare Idea 13542. This version seems to be a 'strong' version, as it demands a higher standard than 'absolute consistency'. Both halves of the condition would have to be established. |
| 13542 | A proof-system is 'absolutely consistent' iff we don't have |-(S)φ for every formula [Bostock] |
| Full Idea: Any system of proof S is said to be 'absolutely consistent' iff it is not the case that for every formula we have |-(S)φ. | |
| From: David Bostock (Intermediate Logic [1997], 4.5) | |
| A reaction: Bostock notes that a sound system will be both 'negation-consistent' (Idea 13541) and absolutely consistent. 'Tonk' systems can be shown to be unsound because the two come apart. |
| 13540 | A set of formulae is 'inconsistent' when there is no interpretation which can make them all true [Bostock] |
| Full Idea: 'Γ |=' means 'Γ is a set of closed formulae, and there is no (standard) interpretation in which all of the formulae in Γ are true'. We abbreviate this last to 'Γ is inconsistent'. | |
| From: David Bostock (Intermediate Logic [1997], 4.5) | |
| A reaction: This is a semantic approach to inconsistency, in terms of truth, as opposed to saying that we cannot prove both p and ¬p. I take this to be closer to the true concept, since you need never have heard of 'proof' to understand 'inconsistent'. |
| 13544 | Inconsistency or entailment just from functors and quantifiers is finitely based, if compact [Bostock] |
| Full Idea: Being 'compact' means that if we have an inconsistency or an entailment which holds just because of the truth-functors and quantifiers involved, then it is always due to a finite number of the propositions in question. | |
| From: David Bostock (Intermediate Logic [1997], 4.8) | |
| A reaction: Bostock says this is surprising, given the examples 'a is not a parent of a parent of b...' etc, where an infinity seems to establish 'a is not an ancestor of b'. The point, though, is that this truth doesn't just depend on truth-functors and quantifiers. |
| 13618 | Compactness means an infinity of sequents on the left will add nothing new [Bostock] |
| Full Idea: The logic of truth-functions is compact, which means that sequents with infinitely many formulae on the left introduce nothing new. Hence we can confine our attention to finite sequents. | |
| From: David Bostock (Intermediate Logic [1997], 5.5) | |
| A reaction: This makes it clear why compactness is a limitation in logic. If you want the logic to be unlimited in scope, it isn't; it only proves things from finite numbers of sequents. This makes it easier to prove completeness for the system. |
| 13358 | Ordinary or mathematical induction assumes for the first, then always for the next, and hence for all [Bostock] |
| Full Idea: The principle of mathematical (or ordinary) induction says suppose the first number, 0, has a property; suppose that if any number has that property, then so does the next; then it follows that all numbers have the property. | |
| From: David Bostock (Intermediate Logic [1997], 2.8) | |
| A reaction: Ordinary induction is also known as 'weak' induction. Compare Idea 13359 for 'strong' or complete induction. The number sequence must have a first element, so this doesn't work for the integers. |
| 13359 | Complete induction assumes for all numbers less than n, then also for n, and hence for all numbers [Bostock] |
| Full Idea: The principle of complete induction says suppose that for every number, if all the numbers less than it have a property, then so does it; it then follows that every number has the property. | |
| From: David Bostock (Intermediate Logic [1997], 2.8) | |
| A reaction: Complete induction is also known as 'strong' induction. Compare Idea 13358 for 'weak' or mathematical induction. The number sequence need have no first element. |
| 7017 | The reductionist programme dispenses with levels of reality [Heil] |
| Full Idea: The reductionist programme dispenses with levels of reality. | |
| From: John Heil (From an Ontological Point of View [2003], 04.3) | |
| A reaction: Fodor, for example, claims that certain causal laws only operate at high levels of reality. I agree with Heil's idea - the notion that there are different realities around here that don't connect properly to one another is philosopher's madness. |
| 7003 | There are levels of organisation, complexity, description and explanation, but not of reality [Heil] |
| Full Idea: We should accept levels of organisation, levels of complexity, levels of description, and levels of explanation, but not the levels of reality favoured by many anti-reductionists. The world is then ontologically, but not analytically, reductive. | |
| From: John Heil (From an Ontological Point of View [2003], Intro) | |
| A reaction: This sounds right to me. The crunch questions seem to be whether the boundaries at higher levels of organisation exist lower down, and whether the causal laws of the higher levels can be translated without remainder into lower level laws. |
| 7045 | Realism says some of our concepts 'cut nature at the joints' [Heil] |
| Full Idea: Realism is sometimes said to involve a commitment to the idea that certain of our concepts, those with respect to which we are realists, 'carve reality at the joints'. | |
| From: John Heil (From an Ontological Point of View [2003], 14.11) | |
| A reaction: Clearly not all concepts cut nature at the joints (e.g. we have concepts of things we know to be imaginary). Personally I am committed to this view of realism. I try very hard to use concepts that cut accurately; why shouldn't I sometimes succeed? |
| 7065 | Anti-realists who reduce reality to language must explain the existence of language [Heil] |
| Full Idea: Anti-realist philosophers, and those who hope to reduce metaphysics to (or replace it with) the philosophy of language, owe the rest of us an account of the ontology of language. | |
| From: John Heil (From an Ontological Point of View [2003], 20.6) | |
| A reaction: A nice turning-the-tables question. In all accounts of relativism, x is usually said to be relative to y. You haven't got proper relativism if you haven't relativised both x and y. But relativised them to what? Nietzsche's 'perspectivism' (Idea 4420)? |
| 7020 | Concepts don't carve up the world, which has endless overlooked or ignored divisions [Heil] |
| Full Idea: Concepts do not 'carve up' the world; the world already contains endless divisions, most of which we remain oblivious to or ignore. | |
| From: John Heil (From an Ontological Point of View [2003], 05.3) | |
| A reaction: Concepts could still carve up the world, without ever aspiring to do a complete job. We carve up the aspects that interest us, but the majority of the carving is in response to natural divisions, not whimsical conventions. |
| 13802 | Relations can be one-many (at most one on the left) or many-one (at most one on the right) [Bostock] |
| Full Idea: A relation is 'one-many' if for anything on the right there is at most one on the left (∀xyz(Rxz∧Ryz→x=y), and is 'many-one' if for anything on the left there is at most one on the right (∀xyz(Rzx∧Rzy→x=y). | |
| From: David Bostock (Intermediate Logic [1997], 8.1) |
| 13543 | A relation is not reflexive, just because it is transitive and symmetrical [Bostock] |
| Full Idea: It is easy to fall into the error of supposing that a relation which is both transitive and symmetrical must also be reflexive. | |
| From: David Bostock (Intermediate Logic [1997], 4.7) | |
| A reaction: Compare Idea 14430! Transivity will take you there, and symmetricality will get you back, but that doesn't entitle you to take the shortcut? |
| 7007 | I think of properties as simultaneously dispositional and qualitative [Heil] |
| Full Idea: Some philosophers who accept that properties are intrinsic features of objects regard them as pure powers, pure dispositionalities; I prefer to think of properties as simultaneously dispositional and qualitative. | |
| From: John Heil (From an Ontological Point of View [2003], Intro) | |
| A reaction: I am uneasy about 'qualitative' as a category, and am inclined to reduce it to being a dispositional power to cause primary and secondary qualities in observers. Roughness is only a power, not a quality, if there are no observers. |
| 7015 | A predicate applies truly if it picks out a real property of objects [Heil] |
| Full Idea: When a predicate applies truly to an object, it does so in virtue of designating a property possessed by that object and by every object to which the predicate truly applies (or would apply). | |
| From: John Heil (From an Ontological Point of View [2003], 03.3) | |
| A reaction: I am sympathetic to Heil's aim of shifting our attention from arbitrary predicates to natural properties, but it won't avoid Fodor's problem (Idea 7014) that all kinds of whimsical predicates will apply 'truly', but fail to pick out anything significant. |
| 7042 | A theory of universals says similarity is identity of parts; for modes, similarity is primitive [Heil] |
| Full Idea: The friend of universals has an account of similarity relations as relations of identity and partial identity; the friend of modes must regard similarity relations as primitive and irreducible. | |
| From: John Heil (From an Ontological Point of View [2003], 14.5) | |
| A reaction: We always seem to be able to ask 'in what respect' a similarity occurs. If similarity is 'primitive and irreducible', we should not be able to analyse and explain a similarity, yet we seem able to. I conclude that Heil is wrong. |
| 7023 | Powers or dispositions are usually seen as caused by lower-level qualities [Heil] |
| Full Idea: The modern default position on dispositionality is that powers or dispositions are higher-level properties objects possess by virtue of those objects' possession of lower-level qualitative (categorical) properties. | |
| From: John Heil (From an Ontological Point of View [2003], 09.2) | |
| A reaction: The new idea which is being floated by Heil, and which I prefer, is that dispositions or powers are basic. A 'quality' is a much more dubious entity than a power. |
| 7025 | Are a property's dispositions built in, or contingently added? [Heil] |
| Full Idea: There is a dispute over whether a property's dispositionality is built into the property or whether it is a contingent add-on. | |
| From: John Heil (From an Ontological Point of View [2003], 09.4) | |
| A reaction: Put that way, the idea that it is built in seems much more plausible. If it is an add-on, an explanation of why that disposition is added to that particular property seems required. If it is built in, it seems legitimate to accept it as a brute fact. |
| 7034 | Universals explain one-over-many relations, and similar qualities, and similar behaviour [Heil] |
| Full Idea: Universals can explain the one-over-many problem, and easily explain similarity relations between objects, and explain the similar behaviour of similar objects. | |
| From: John Heil (From an Ontological Point of View [2003], 13.1) | |
| A reaction: A useful summary. If you accept it, you seem to be faced with a choice between Plato (who has universals existing independently of particulars) and Armstrong (who makes them real, but existing only in particulars). |
| 7039 | How could you tell if the universals were missing from a world of instances? [Heil] |
| Full Idea: Imagine a pair of worlds, one in which there are the universals and their instances and one in which there are just the instances (a world of modes). How would the absence of universals make itself felt? | |
| From: John Heil (From an Ontological Point of View [2003], 13.7) | |
| A reaction: A nice question for Plato, very much in the spirit of Aristotle's string of questions. Compare 'suppose the physics remained, but someone removed the laws'. Either chaos ensues, or you realise they were redundant. Same with Forms. |
| 7009 | Similarity among modes will explain everthing universals were for [Heil] |
| Full Idea: My contention is that similarity among modes can do the job universals are conventionally postulated to do. | |
| From: John Heil (From an Ontological Point of View [2003], Intro) | |
| A reaction: See Idea 4441 for Russell's nice objection to this view. The very process by which we observes similarities (as assess their degrees) needs to be explained by any adequate theory of properties or universals. |
| 7041 | Similar objects have similar properties; properties are directly similar [Heil] |
| Full Idea: Objects are similar by virtue of possessing similar properties; properties, in contrast, are not similar in virtue of anything. | |
| From: John Heil (From an Ontological Point of View [2003], 14.2) | |
| A reaction: I am not sure if I can understand the concept of similarity if there is no answer to the question 'In what respect?' I suppose David Hume is happy to take resemblance as given and basic, but it could be defined as 'sharing identical properties'. |
| 7032 | Objects join sets because of properties; the property is not bestowed by set membership [Heil] |
| Full Idea: The set of red objects is the set of objects possessing a property: being red. Objects are members of the set in virtue of possessing this property; they do not possess the property in virtue of belonging to the set. | |
| From: John Heil (From an Ontological Point of View [2003], 12.2) | |
| A reaction: This seems to be a very effective denial of the claim that universals are sets. However, if 'being a Londoner' counts as a property, you can only have it by joining the London set. Being tall is more fundamental than being a Londoner. |
| 7008 | Trope theorists usually see objects as 'bundles' of tropes [Heil] |
| Full Idea: Philosophers identifying themselves as trope theorists have, by and large, accepted some form of the 'bundle theory' of objects: an object is a bundle of compresent tropes. | |
| From: John Heil (From an Ontological Point of View [2003], Intro) | |
| A reaction: This view eliminates anything called 'matter' or 'substance' or a 'bare particular'. I think I agree with Heil that this doesn't give a coherent picture, as properties seem to be 'of' something, and bundles always raise the question of what unites them. |
| 7018 | Objects are substances, which are objects considered as the bearer of properties [Heil] |
| Full Idea: I think of objects as substances, and a substance is an object considered as a bearer of properties. | |
| From: John Heil (From an Ontological Point of View [2003], 04.2) | |
| A reaction: This is an area of philosophy I always find disconcerting, where an account of how we should see objects seems to have no connection at all to what physicists report about objects. 'Considered as' seems to make substances entirely conventional. |
| 7019 | Maybe there is only one substance, space-time or a quantum field [Heil] |
| Full Idea: It would seem distinctly possible that there is but a single substance: space-time or some all-encompassing quantum field. | |
| From: John Heil (From an Ontological Point of View [2003], 05.2) | |
| A reaction: This would at least meet my concern that philosophers' 'substances' don't seem to connect to what physicists talk about. I wonder if anyone knows what a 'quantum field' is? The clash between relativity and quantum theory is being alluded to. |
| 7046 | Rather than 'substance' I use 'objects', which have properties [Heil] |
| Full Idea: I prefer the more colloquial 'object' to the traditional term 'substance'. An object can be regarded as a possessor of properties: as something that is red, spherical and pungent, for instance. | |
| From: John Heil (From an Ontological Point of View [2003], 15.3) | |
| A reaction: A nice move, but it seems to beg the question of 'what is it that has the properties?' Objects and substances do two different jobs in our ontology. Heil is just refusing to discuss what it is that has properties. |
| 7047 | Statues and bronze lumps have discernible differences, so can't be identical [Heil] |
| Full Idea: Applications of the principle of the indiscernibility of identicals apparently obliges us to distinguish the statue and the lump of bronze making it up. | |
| From: John Heil (From an Ontological Point of View [2003], 16.3) | |
| A reaction: In other words, statues and lumps of bronze have different properties. It is a moot point, though, whether there are any discernible differences between that statue at time t and its constituting lump of bronze at time t. |
| 7048 | Do we reduce statues to bronze, or eliminate statues, or allow statues and bronze? [Heil] |
| Full Idea: Must we choose between reductionism (the statue is the lump of bronze), eliminativism (there are no statues, only statue-shaped lumps of bronze), and a commitment to coincident objects? | |
| From: John Heil (From an Ontological Point of View [2003], 16.5) | |
| A reaction: (Heil goes on to offer his own view). Coincident objects sounds the least plausible view. Modern statues are only statues if we see them that way, but a tree is definitely a tree. Trenton Merricks is good on eliminativism. |
| 13847 | If non-existent things are self-identical, they are just one thing - so call it the 'null object' [Bostock] |
| Full Idea: If even non-existent things are still counted as self-identical, then all non-existent things must be counted as identical with one another, so there is at most one non-existent thing. We might arbitrarily choose zero, or invent 'the null object'. | |
| From: David Bostock (Intermediate Logic [1997], 8.6) |
| 13820 | The idea that anything which can be proved is necessary has a problem with empty names [Bostock] |
| Full Idea: The common Rule of Necessitation says that what can be proved is necessary, but this is incorrect if we do not permit empty names. The most straightforward answer is to modify elementary logic so that only necessary truths can be proved. | |
| From: David Bostock (Intermediate Logic [1997], 8.4) |
| 7030 | Properties don't possess ways they are, because that just is the property [Heil] |
| Full Idea: Objects possess properties, but I am sceptical of the idea that properties possess properties; just as a property is a way some object is, a property of a property would be a way a property is, but that is just the property itself. | |
| From: John Heil (From an Ontological Point of View [2003], 12.1) | |
| A reaction: This is quite a good defence of the idea that properties are qualities as well as dispositions. However, if we make the qualities of properties into secondary qualities, and the dispositions into primary qualities, the absurdity melts away. |
| 7028 | If properties were qualities without dispositions, they would be undetectable [Heil] |
| Full Idea: A pure quality, a property altogether lacking in dispositionality, would be undetectable and would, in one obvious sense, make no difference to its possessor. | |
| From: John Heil (From an Ontological Point of View [2003], 11.4) | |
| A reaction: This seems to be a very forceful and simple reason why we cannot view properties simply as qualities of things. Heil wants properties to be dispositions and qualities; personally I would vote for them just being dispositions or powers. |
| 7029 | Can we distinguish the way a property is from the property? [Heil] |
| Full Idea: It is not clear to me that we easily distinguish ways a property is from the property itself. | |
| From: John Heil (From an Ontological Point of View [2003], 11.6) | |
| A reaction: To defend properties as qualities, he is confusing ontology and epistemology. Presumably he means by 'ways a property is' what I would prefer to call 'ways a property seems to be'. I don't believe a smell is simply what it seems to be. |
| 7051 | Objects only have secondary qualities because they have primary qualities [Heil] |
| Full Idea: Secondary qualities are not distinct from primary qualities: an object's possession of a given secondary quality is a matter of its possession of certain complex primary qualities. | |
| From: John Heil (From an Ontological Point of View [2003], 17.3) | |
| A reaction: The bottom line here is that, if essentialism is right, colours are not properties at all (see Idea 5456). Heil wants to subsume secondary properties within primary properties. I think we should sharply distinguish them. |
| 7044 | Secondary qualities are just primary qualities considered in the light of their effect on us [Heil] |
| Full Idea: Secondary qualities are just ordinary properties - roughly, Locke's primary qualities - considered in the light of their effects on us. | |
| From: John Heil (From an Ontological Point of View [2003], 14.10) | |
| A reaction: Unconvincing. If they only acquire their ontological status as primary qualities if they have to be considered in relation to something (us), then that is not a primary quality. |
| 7052 | Colours aren't surface properties, because of radiant sources and the colour of the sky [Heil] |
| Full Idea: Theories that take colours to be properties of the surfaces of objects have difficulty accounting for a host of phenomena including coloured light emitted by radiant sources and so-called film colours (the colour of the sky, for instance). | |
| From: John Heil (From an Ontological Point of View [2003], 17.4) | |
| A reaction: Personally I never thought that colours might be actual properties of surfaces, but it is nice to have spelled out a couple of instances that make it very implausible. Neon and sodium lights I take to be examples of the first case. |
| 7053 | Treating colour as light radiation has the implausible result that tomatoes are not red [Heil] |
| Full Idea: Theories that tie colours to features of light radiation deal with radiant and diffused colours, but yield implausible results for objects; tomatoes are not red, on such a view, but merely reflect red light. | |
| From: John Heil (From an Ontological Point of View [2003], 17.4) | |
| A reaction: I see absolutely no problem with the philosophical denial that tomatoes are actually red, while continuing to use 'red' of tomatoes in the normal way. When we analyse our processes of knowledge acquisition, we must give up 'common sense'. |
| 19730 | Epistemic virtues: love of knowledge, courage, caution, autonomy, practical wisdom... [Kvanvig] |
| Full Idea: Virtue theorists may focus on the particular habits or virtues of successful cognizers, such as love of knowledge, firmness, courage and caution, humility, autonomy, generosity, and practical wisdom. | |
| From: Jonathan Kvanvig (Virtue Epistemology [2011], III) | |
| A reaction: [He cites Roberts and Wood 2007] It is interesting that most of these virtues do not merely concern cognition. How about diligence, self-criticism, flexibility...? |
| 19731 | If epistemic virtues are faculties or powers, that doesn't explain propositional knowledge [Kvanvig] |
| Full Idea: Conceiving of the virtues in terms of faculties or powers doesn't help at all with the problem of accounting for propositional knowledge. | |
| From: Jonathan Kvanvig (Virtue Epistemology [2011], IV B) | |
| A reaction: It always looks as if epistemic virtues are a little peripheral to the main business of knowledge, which is getting beliefs to be correct and well-founded. Given that epistemic saints make occasional mistakes, talk of virtues can't be enough. |
| 19732 | The value of good means of attaining truth are swamped by the value of the truth itself [Kvanvig] |
| Full Idea: The Swamping Problem is that the value of truth swamps the value of additional features of true beliefs which are only instrumentally related to them. True belief is no more valuable if one adds a feature valuable for getting one to the truth. | |
| From: Jonathan Kvanvig (Virtue Epistemology [2011], IV B) | |
| A reaction: His targets here are reliabilism and epistemic virtues. Kvanvig's implication is that the key to understanding the nature of knowledge is to pinpoint why we value it so much. |
| 7066 | If the world is just texts or social constructs, what are texts and social constructs? [Heil] |
| Full Idea: For those who regard the world as text or a social construct, are texts and social constructs real entities? If they are, what are they? | |
| From: John Heil (From an Ontological Point of View [2003], 20.6) | |
| A reaction: A nice turn-the-tables question. The oldest attacks of all on scepticism and relativism consist of showing that the positions themselves rest on knowledge or truth. Nietzsche may be the best model for relativists. E.g. Idea 4420. |
| 7021 | If the world is theory-dependent, the theories themselves can't be theory-dependent [Heil] |
| Full Idea: If the world is somehow theory-dependent, this implies, on pain of a regress, that theories are not theory-dependent. | |
| From: John Heil (From an Ontological Point of View [2003], 06.4) | |
| A reaction: I am not sure where this puts the ontology of theories, but this is a nice question, of a type which never seems to occur to your more simple-minded relativist. |
| 7026 | Science is sometimes said to classify powers, neglecting qualities [Heil] |
| Full Idea: The sciences are sometimes said to be in the business of identifying and classifying powers; the mass of an electron, its spin and charge, could be regarded as powers possessed by the electron; science is silent on an electron's qualities. | |
| From: John Heil (From an Ontological Point of View [2003], 11.2) | |
| A reaction: Heil raises the possibility that qualities are real, despite the silence of science; he wants colour to be a real quality. I like the simpler version of science. Qualities are the mental effects of powers; there exist substances, powers and effects. |
| 7060 | One form of explanation is by decomposition [Heil] |
| Full Idea: One form of explanation is by decomposition. | |
| From: John Heil (From an Ontological Point of View [2003], 19.8) | |
| A reaction: This is a fancy word for taking it apart, presumably to see how it works, which implies a functional explanation, rather than to see what it is made of, which seeks an ontological explanation. Simply 'decomposing' something wouldn't in itself explain. |
| 7010 | Dispositionality provides the grounding for intentionality [Heil] |
| Full Idea: Dispositionality provides the grounding for intentionality. | |
| From: John Heil (From an Ontological Point of View [2003], Intro) | |
| A reaction: This is a view with which I am sympathetic, though I am not sure if it explains anything. It would be necessary to identify a disposition of basic matter that could be built up into the disposition of a brain to think about things. |
| 7054 | Intentionality now has internalist (intrinsic to thinkers) and externalist (environment or community) views [Heil] |
| Full Idea: Nowadays philosophers concerned with intentionality divide into two camps. Internalists epitomise a traditional approach to thought, as intrinsic features of thinkers; externalists say it depends on contextual factors (environment or community). | |
| From: John Heil (From an Ontological Point of View [2003], 18.2) | |
| A reaction: This is basic to understanding modern debates (those that grow out of Putnam's Twin Earth). Externalism is fashionable, but I am reluctant to shake off my quaint internalism. Start by separating strict and literal meaning from speaker's meaning. |
| 7011 | Qualia are not extra appendages, but intrinsic ingredients of material states and processes [Heil] |
| Full Idea: Properties of conscious experience, the so-called qualia, are not dangling appendages to material states and processes but intrinsic ingredients of those states and processes. | |
| From: John Heil (From an Ontological Point of View [2003], Intro) | |
| A reaction: Personally I am inclined to the view that qualia are intrinsic to the processes and NOT to the 'states'. Heil must be right, though. I am sure qualia are not just epiphenomena - they are too useful. |
| 7061 | Philosophers' zombies aim to show consciousness is over and above the physical world [Heil] |
| Full Idea: Philosophers' zombies (invented by Robert Kirk) differ from the zombies of folklore; they are intended to make clear the idea that consciousness is an addition of being, something 'over and above' the physical world. | |
| From: John Heil (From an Ontological Point of View [2003], 20.1 n1) | |
| A reaction: The famous defender of zombies is David Chalmers. You can't believe in zombies if you believe (as I do) that 'the physical entails the mental'. Could there be redness without something that is red? If consciousness is extra, what is conscious? |
| 7063 | Zombies are based on the idea that consciousness relates contingently to the physical [Heil] |
| Full Idea: The possibility of zombies is founded on the idea that consciousness is related contingently to physical states and processes. | |
| From: John Heil (From an Ontological Point of View [2003], 20.3) | |
| A reaction: The question is, how do you decide whether the relationship is contingent or necessary? Hence the interest in whether conceivability entails possibility. Kripke attacks the idea of contingent identity, pointing towards necessity, and away from zombies. |
| 7064 | Functionalists deny zombies, since identity of functional state means identity of mental state [Heil] |
| Full Idea: Functionalists deny that zombies are possible since states of mind (including conscious states) are purely functional states. If two agents are in the same functional state, regardless of qualitative difference, they are in the same mental state. | |
| From: John Heil (From an Ontological Point of View [2003], 20.5) | |
| A reaction: In its 'brief' form this idea begins to smell of tautology. Only the right sort of functional state would entail a mental state, and how else can that functional state be defined, apart from its leading to a mental state? |
| 7027 | Functionalists say objects can be the same in disposition but differ in quality [Heil] |
| Full Idea: A central tenet of functionalism is that objects can be dispositionally indiscernible but differ qualitatively as much as you please. | |
| From: John Heil (From an Ontological Point of View [2003], 11.3) | |
| A reaction: This refers to the multiple realisability of functions. Presumably we reconcile essentialism with the functionalist view by saying that dispositions result from combinations of qualities. A unique combination of qualities will necessitate a disposition. |
| 7062 | Functionalism cannot explain consciousness just by functional organisation [Heil] |
| Full Idea: Functionalism has been widely criticized on the grounds that it is implausible to think that functional organization alone could suffice for conscious experience. | |
| From: John Heil (From an Ontological Point of View [2003], 20.2) | |
| A reaction: He cites Block's 'Chinese Mind' as an example. The obvious reply is that you can't explain consciousness with a lump of meat, or with behaviour, or with an anomalous property, or even with a non-physical substance. |
| 7059 | The 'explanatory gap' is used to say consciousness is inexplicable, at least with current concepts [Heil] |
| Full Idea: The expression 'explanatory gap' was coined by Joseph Levine in 1983. McGinn and Chalmers have invoked it in defence of the view that consciousness is physically inexplicable, and Nagel that it is inexplicable given existing conceptual resources. | |
| From: John Heil (From an Ontological Point of View [2003], 19.8 n14) | |
| A reaction: Coining a few concepts isn't going to help, but discovering more about the brain might. With computer simulations we will 'see' more of the physical end of thought. Psychologists may break thought down into physically more manageable components. |
| 7012 | If a car is a higher-level entity, distinct from its parts, how could it ever do anything? [Heil] |
| Full Idea: If we regard a Volvo car as a higher-level entity with its own independent reality, something distinct from its constituents (arranged in particular ways and variously connected to other things), we render mysterious how Volvos could do anything at all. | |
| From: John Heil (From an Ontological Point of View [2003], 02.3) | |
| A reaction: This seems to me perhaps the key reason why we have to be reductionists. The so-called 'bridge laws' from mind to brain are not just needed to explain the mind, they are also essential to show how a mind would cause behaviour. |
| 7043 | Multiple realisability is actually one predicate applying to a diverse range of properties [Heil] |
| Full Idea: Cases of multiple realisability are typically cases in which some predicate ('is red', 'is in pain') applies to an object in virtue of that object's possession of any of a diverse range of properties. | |
| From: John Heil (From an Ontological Point of View [2003], 14.8) | |
| A reaction: If the properties are diverse, why does one predicate apply to them? I take it that in the case of the pain, the predicate is ambiguous in applying to the behaviour or the phenomenal property. Same behaviour is possible with many qualia. |
| 7058 | Externalism is causal-historical, or social, or biological [Heil] |
| Full Idea: Some externalists focus on causal-historical connections, others emphasise social matters (especially thinkers' linguistic communities), still others focus on biological function. | |
| From: John Heil (From an Ontological Point of View [2003], 18.5 n6) | |
| A reaction: Helpful. The social view strikes me as the one to take most seriously (allowing for contextual views of justification, and for the social role of experts). The problem is to combine the social view with realism and a robust view of truth. |
| 7057 | Intentionality is based in dispositions, which are intrinsic to agents, suggesting internalism [Heil] |
| Full Idea: I suggest that intentionality is grounded in the dispositionalities of agents. Dispositions are intrinsic to agents, so this places me on the side of the internalists and against the externalists. | |
| From: John Heil (From an Ontological Point of View [2003], 18.4) | |
| A reaction: I think this is a key idea, and the right view. The key question is whether we see intentionality as active or passive. The externalist view seems to see the brain as a passive organ which the world manipulates. If the brain is active, what is it doing? |
| 7013 | The Picture Theory claims we can read reality from our ways of speaking about it [Heil] |
| Full Idea: The theory of language which I designate the 'Picture Theory' says that language pictures reality in roughly the sense that we can 'read off' features of reality from our ways of speaking about it. | |
| From: John Heil (From an Ontological Point of View [2003], 03.2) | |
| A reaction: Heil, quite rightly, attacks this view very strongly. I think of it as the great twentieth century philosophical heresy, that leads to shocking views like relativism and anti-realism. |
| 13363 | A (modern) predicate is the result of leaving a gap for the name in a sentence [Bostock] |
| Full Idea: A simple way of approaching the modern notion of a predicate is this: given any sentence which contains a name, the result of dropping that name and leaving a gap in its place is a predicate. Very different from predicates in Aristotle and Kant. | |
| From: David Bostock (Intermediate Logic [1997], 3.2) | |
| A reaction: This concept derives from Frege. To get to grips with contemporary philosophy you have to relearn all sorts of basic words like 'predicate' and 'object'. |
| 7002 | If propositions are states of affairs or sets of possible worlds, these lack truth values [Heil] |
| Full Idea: When pressed, philosophers will describe propositions as states of affairs or sets of possible worlds. But wait! Neither sets of possible worlds nor states of affairs - electrons being negatively charged, for instance - have truth values. | |
| From: John Heil (From an Ontological Point of View [2003], Intro) | |
| A reaction: I'm not sure that I see a problem. A pure proposition, expressed as, say "there is a giraffe on the roof" only acquires a truth value at the point where you assert it or believe it. There IS a possible world where there is a giraffe on the roof. |
| 7016 | The standard view is that causal sequences are backed by laws, and between particular events [Heil] |
| Full Idea: The notion that every causal sequence if backed by a law, like the idea that causation is a relation among particular events, forms a part of philosophy's Humean heritage. | |
| From: John Heil (From an Ontological Point of View [2003], 04.3) | |
| A reaction: This nicely pinpoints a view that needs to come under attack. I take the view that there are no 'laws' - other than the regularities in behaviour that result from the interaction of essential dispositional properties. Essences don't need laws. |
| 7036 | The real natural properties are sparse, but there are many complex properties [Heil] |
| Full Idea: I am sympathetic to the idea that the real properties are 'sparse'; ...but if, in counting kinds of property, we include complex properties as well as simple properties, the image of sparseness evaporates. | |
| From: John Heil (From an Ontological Point of View [2003], 13.4) | |
| A reaction: This seems right to me, and invites the obvious question of which are the sparse real properties. Presumably we let the physicists tell us that, though Heil wants to include qualities like phenomenal colour, which physicists ignore. |