30 ideas
| 7786 | Propositional logic handles negation, disjunction, conjunction; predicate logic adds quantifiers, predicates, relations [Girle] |
| Full Idea: Propositional logic can deal with negation, disjunction and conjunction of propositions, but predicate logic goes beyond it to deal with quantifiers, predicates and relations. | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 1.1) | |
| A reaction: This is on the first page of an introduction to the next stage, which is to include modal notions like 'must' and 'possibly'. |
| 7798 | There are three axiom schemas for propositional logic [Girle] |
| Full Idea: The axioms of propositional logic are: A→(B→A); A→(B→C)→(A→B)→(A→C) ; and (¬A→¬B)→(B→A). | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 6.5) |
| 7799 | Proposition logic has definitions for its three operators: or, and, and identical [Girle] |
| Full Idea: The operators of propositional logic are defined as follows: 'or' (v) is not-A implies B; 'and' (ampersand) is not A-implies-not-B; and 'identity' (three line equals) is A-implies-B and B-implies-A. | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 6.5) |
| 7797 | Axiom systems of logic contain axioms, inference rules, and definitions of proof and theorems [Girle] |
| Full Idea: An axiom system for a logic contains three elements: a set of axioms; a set of inference rules; and definitions for proofs and theorems. There are also definitions for the derivation of conclusions from sets of premises. | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 6.5) |
| 7794 | There are seven modalities in S4, each with its negation [Girle] |
| Full Idea: In S4 there are fourteen modalities: no-operator; necessarily; possibly; necessarily-possibly; possibly-necessarily; necessarily-possibly-necessarily; and possibly-necessarily-possibly (each with its negation). | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 3.5) | |
| A reaction: This is said to be 'more complex' than S5, but also 'weaker'. |
| 7793 | ◊p → □◊p is the hallmark of S5 [Girle] |
| Full Idea: The critical formula that distinguishes S5 from all others is: ◊p → □◊p. | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 3.3) | |
| A reaction: If it is possible that it is raining, then it is necessary that it is possible that it is raining. But if it is possible in this world, how can that possibility be necessary in all possible worlds? |
| 7795 | S5 has just six modalities, and all strings can be reduced to those [Girle] |
| Full Idea: In S5 there are six modalities: no-operator; necessarily; and possibly (and their negations). In any sequence of operators we may delete all but the last to gain an equivalent formula. | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 3.5) | |
| A reaction: Such drastic simplification seems attractive. Is there really no difference, though, between 'necessarily-possibly', 'possibly-possibly' and just 'possibly'? Could p be contingently possible in this world, and necessarily possible in another? |
| 7787 | Possible worlds logics use true-in-a-world rather than true [Girle] |
| Full Idea: In possible worlds logics a statement is true-in-a-world rather than just true. | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 1.1) | |
| A reaction: This sounds relativist, but I don't think it is. It is the facts which change, not the concept of truth. So 'donkeys can talk' may be true in a world, but not in the actual one. |
| 7788 | Modal logic has four basic modal negation equivalences [Girle] |
| Full Idea: The four important logical equivalences in modal logic (the Modal Negation equivalences) are: ¬◊p↔□¬p, ◊¬p↔¬□p, □p↔¬◊¬p, and ◊p↔¬□¬p. | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 1.2) | |
| A reaction: [Possibly is written as a diamond, necessarily a square] These are parallel to a set of equivalences between quantifiers in predicate logic. They are called the four 'modal negation (MN) equivalences'. |
| 7796 | Modal logics were studied in terms of axioms, but now possible worlds semantics is added [Girle] |
| Full Idea: Modal logics were, for a long time, studied in terms of axiom systems. The advent of possible worlds semantics made it possible to study them in a semantic way as well. | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 6.5) |
| 13479 | Given that thinking aims at truth, logic gives universal rules for how to do it [Burge] |
| Full Idea: The laws of logic - which are constituted by atemporal thoughts and atemporal subject matter - provide universal prescriptions of how one ought to think, given that one's thinking has the function of attaining truth. | |
| From: Tyler Burge (Frege on Knowing the Third Realm [1992], p.316) | |
| A reaction: Burge is giving, and endorsing, Frege's view. Burge is fighting a rearguard action, when logical systems keep proliferating. See Idea 10282. I sympathise with the dream of Burge and Frege. |
| 7789 | Necessary implication is called 'strict implication'; if successful, it is called 'entailment' [Girle] |
| Full Idea: Necessary implication is often called 'strict implication'. The sort of strict implication found in valid arguments, where the conjunction of the premises necessarily implies the conclusion, is often called 'entailment'. | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 1.2) | |
| A reaction: These are basic concept for all logic. |
| 8132 | We now have a much more sophisticated understanding of logical form in language [Burge] |
| Full Idea: The second half of the twentieth century has seen the development of a vastly more sophisticated sense of logical form, as applied to natural languages. | |
| From: Tyler Burge (Philosophy of Mind: 1950-2000 [2005], p.462) | |
| A reaction: Burge cites this as one of the three big modern developments (along with the critique of logical positivism, and direct reference/anti-individualism). Vagueness may be the last frontier for this development. |
| 7790 | If an argument is invalid, a truth tree will indicate a counter-example [Girle] |
| Full Idea: The truth trees method for establishing the validity of arguments and formulas is easy to use, and has the advantage that if an argument or formula is not valid, then a counter-example can be retrieved from the tree. | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 1.4) |
| 17622 | We come to believe mathematical propositions via their grounding in the structure [Burge] |
| Full Idea: A deeper justification for believing in [mathematical] propositions [apart from pragmatism] lies in finding their place in a logicist proof structure, by understanding the grounds within this structure that support them. | |
| From: Tyler Burge (Frege on Knowing the Foundations [1998], 3) | |
| A reaction: This generalises to doubting something until you see what grounds it. |
| 16901 | The equivalent algebra model of geometry loses some essential spatial meaning [Burge] |
| Full Idea: Geometrical concepts appear to depend in some way on a spatial ability. Although one can translate geometrical propositions into algebraic ones and produce equivalent models, the meaning of the propositions seems to me to be thereby lost. | |
| From: Tyler Burge (Frege on Apriority (with ps) [2000], 4) | |
| A reaction: I think this is a widely held view nowadays. Giaquinto has a book on it. A successful model of something can't replace it. Set theory can't replace arithmetic. |
| 9159 | You can't simply convert geometry into algebra, as some spatial content is lost [Burge] |
| Full Idea: Although one can translate geometrical propositions into algebraic ones and produce equivalent models, the meaning of geometrical propositions seems to me to be thereby lost. Pure geometry involves spatial content, even if abstracted from physical space. | |
| From: Tyler Burge (Frege on Apriority [2000], IV) | |
| A reaction: This supports Frege's view (against Quine) that geometry won't easily fit into the programme of logicism. I agree with Burge. You would be focusing on the syntax of geometry, and leaving out the semantics. |
| 16902 | Peano arithmetic requires grasping 0 as a primitive number [Burge] |
| Full Idea: In the Peano axiomatisation, arithmetic seems primitively to involve the thought that 0 is a number. | |
| From: Tyler Burge (Frege on Apriority (with ps) [2000], 5) | |
| A reaction: Burge is pointing this out as a problem for Frege, for whom only the logic is primitive. |
| 7800 | Analytic truths are divided into logically and conceptually necessary [Girle] |
| Full Idea: It has been customary to see analytic truths as dividing into the logically necessary and the conceptually necessary. | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 7.3) | |
| A reaction: I suspect that this neglected distinction is important in discussions of Quine's elimination of the analytic/synthetic distinction. Was Quine too influenced by what is logically necessary, which might shift with a change of axioms? |
| 7801 | Possibilities can be logical, theoretical, physical, economic or human [Girle] |
| Full Idea: Qualified modalities seem to form a hierarchy, if we say that 'the possibility that there might be no hunger' is possible logically, theoretically, physically, economically, and humanly. | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 7.3) | |
| A reaction: Girle also mentions conceptual possibility. I take 'physically' to be the same as 'naturally'. I would take 'metaphysically' possible to equate to 'theoretically' rather than 'logically'. Almost anything might be logically possible, with bizarre logic. |
| 7792 | A world has 'access' to a world it generates, which is important in possible worlds semantics [Girle] |
| Full Idea: When one world generates another then it has 'access' to the world it generated. The accessibility relation between worlds is very important in possible worlds semantics. | |
| From: Rod Girle (Modal Logics and Philosophy [2000], 3.2) | |
| A reaction: This invites the obvious question what is meant by 'generates'. |
| 16892 | Is apriority predicated mainly of truths and proofs, or of human cognition? [Burge] |
| Full Idea: Whereas Leibniz and Frege predicate apriority primarily of truths (or more fundamentally, proofs of truths), Kant predicates apriority primarily of cognition and the employment of representations. | |
| From: Tyler Burge (Frege on Apriority (with ps) [2000], 1) |
| 9382 | Subjects may be unaware of their epistemic 'entitlements', unlike their 'justifications' [Burge] |
| Full Idea: I call 'entitlement' (as opposed to justification) the epistemic rights or warrants that need not be understood by or even be accessible to the subject. | |
| From: Tyler Burge (Content Preservation [1993]), quoted by Paul Boghossian - Analyticity Reconsidered §III | |
| A reaction: I espouse a coherentism that has both internal and external components, and is mediated socially. In Burge's sense, animals will sometimes have 'entitlement'. I prefer, though, not to call this 'knowledge'. 'Entitled true belief' is good. |
| 8126 | Anti-individualism says the environment is involved in the individuation of some mental states [Burge] |
| Full Idea: Anti-individualism is the view that not all of an individual's mental states and events can be type-individuated independently of the nature of the entities in the individual's physical or social environment environment. | |
| From: Tyler Burge (Philosophy of Mind: 1950-2000 [2005], p.453) | |
| A reaction: While the Twin Earth experiment emphasises the physical environment, Burge has been responsible for emphasising the social environment. The suspicion is that the whole concept of 'individual' minds will collapse on this view. |
| 8127 | Broad concepts suggest an extension of the mind into the environment (less computer-like) [Burge] |
| Full Idea: Certain thought experiments made trouble for standard functionalism, which limits input/output to the surface of an individual; proposals to extend this into the environment reduces the reliance on a computer paradigm, but increases complexity. | |
| From: Tyler Burge (Philosophy of Mind: 1950-2000 [2005], p.454) | |
| A reaction: [He has the Twin Earth experiment in mind] The jury is out on this, but it looks a bit of a slippery slope. Accounts of action and responsibility need a fairly sharp concept of an individual. Externalism begins to look like just a new scepticism. |
| 8129 | Anti-individualism may be incompatible with some sorts of self-knowledge [Burge] |
| Full Idea: The idea of anti-individualism raised problems about self-knowledge. The question is whether anti-individualism is compatible with some sort of authoritative or privileged warrant for certain types of self-knowledge. | |
| From: Tyler Burge (Philosophy of Mind: 1950-2000 [2005], p.457) | |
| A reaction: [See under 'Nature of Minds' for 'Anti-individualism'] The thought is that if your mind is not entirely in your head, you can no longer be an expert on it. It might go the other way: obviously we can be self-experts, so anti-individualism is wrong. |
| 8131 | Some qualities of experience, like blurred vision, have no function at all [Burge] |
| Full Idea: There appear to be qualitative aspects of experience that have no function in the life of the organism. They constitute dysfunction or noise. Blurriness in a visual experience is an example. | |
| From: Tyler Burge (Philosophy of Mind: 1950-2000 [2005], p.460) | |
| A reaction: The best account of blurred vision would seem to be adverbial - I see 'in a blurred way' (nay, blurredly). Hence maybe blurred vision is functional, but it just isn't functioning very well. |
| 3115 | Are meaning and expressed concept the same thing? [Burge, by Segal] |
| Full Idea: It is Burge's view that what a word means should be distinguished from the concept it expresses. | |
| From: report of Tyler Burge (Frege on Extensions from Concepts [1984]) by Gabriel M.A. Segal - A Slim Book about Narrow Content 3.2 | |
| A reaction: Presumably the immediate meaning (e.g. of 'arthritis') is socially determined, while the concept is fixed by history? Or what? |
| 14349 | If there are no finks or antidotes at the fundamental level, the laws can't be ceteris paribus [Burge, by Corry] |
| Full Idea: Bird argues that there are no finks at the fundamental level, and unlikely to be any antidotes. It then follows that laws at the fundamental level will all be strict - not ceteris paribus - laws. | |
| From: report of Tyler Burge (Intellectual Norms and Foundations of Mind [1986]) by Richard Corry - Dispositional Essentialism Grounds Laws of Nature? 3 | |
| A reaction: [Bird's main target is Nancy Cartwright 1999] This is a nice line of argument. Isn't part of the ceteris paribus problem that two fundamental laws might interfere with one another? |
| 1513 | The Egyptians were the first to say the soul is immortal and reincarnated [Herodotus] |
| Full Idea: The Egyptians were the first to claim that the soul of a human being is immortal, and that each time the body dies the soul enters another creature just as it is being born. | |
| From: Herodotus (The Histories [c.435 BCE], 2.123.2) |