50 ideas
| 11051 | Frege's logical approach dominates the analytical tradition [Hanna] |
| Full Idea: Pure logic constantly controls Frege's philosophy, and in turn Frege's logically oriented philosophy constantly controls the analytic tradition. | |
| From: Robert Hanna (Rationality and Logic [2006], 1.1) | |
| A reaction: Hanna seeks to reintroduce the dreaded psychological aspect of logic, and I say 'good for him'. |
| 9136 | The paradox of analysis says that any conceptual analysis must be either trivial or false [Sorensen] |
| Full Idea: The paradox of analysis says if a conceptual analysis states exactly what the original statement says, then the analysis is trivial; if it says something different from the original, then the analysis is mistaken. All analyses are trivial or false. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 8.5) | |
| A reaction: [source is G.E. Moore] Good analyses typically give explanations, or necessary and sufficient conditions, or inferential relations. At their most trivial they at least produce a more profound dictionary than your usual lexicographer. Not guilty. |
| 11054 | Scientism says most knowledge comes from the exact sciences [Hanna] |
| Full Idea: Scientism says that the exact sciences are the leading sources of knowledge about the world. | |
| From: Robert Hanna (Rationality and Logic [2006], 1.2) | |
| A reaction: I almost agree, but I would describe the exact sciences as the chief 'evidence' for our knowledge, with the chief 'source' being our own ability to make coherent sense of the evidence. Exact sciences rest on mathematics. |
| 9131 | Two long understandable sentences can have an unintelligible conjunction [Sorensen] |
| Full Idea: If there is an upper bound on the length of understandable sentences, then two understandable sentences can have an unintelligible conjunction. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 6.4) | |
| A reaction: Not a huge paradox about the use of the word 'and', perhaps, but a nice little warning to be clear about what is being claimed before you cheerfully assert a screamingly obvious law of thought, such as conjunction. |
| 11070 | 'Denying the antecedent' fallacy: φ→ψ, ¬φ, so ¬ψ [Hanna] |
| Full Idea: The fallacy of 'denying the antecedent' is of the form φ→ψ, ¬φ, so ¬ψ. | |
| From: Robert Hanna (Rationality and Logic [2006], 5.4) |
| 11071 | 'Affirming the consequent' fallacy: φ→ψ, ψ, so φ [Hanna] |
| Full Idea: The fallacy of 'affirming the consequent' is of the form φ→ψ, ψ, so φ. | |
| From: Robert Hanna (Rationality and Logic [2006], 5.4) |
| 11088 | We can list at least fourteen informal fallacies [Hanna] |
| Full Idea: Informal fallacies: appeals to force, circumstantial factors, ignorance, pity, popular consensus, authority, generalisation, confused causes, begging the question, complex questions, irrelevance, equivocation, black-and-white, slippery slope etc. | |
| From: Robert Hanna (Rationality and Logic [2006], 7.3) |
| 11059 | Circular arguments are formally valid, though informally inadmissible [Hanna] |
| Full Idea: A circular argument - one whose conclusion is to be found among its premises - is inadmissible in most informal contexts, even though it is formally valid. | |
| From: Robert Hanna (Rationality and Logic [2006], 2.1) | |
| A reaction: Presumably this is a matter of conversational implicature - that you are under a conventional obligation to say things which go somewhere, rather than circling around their starting place. |
| 11089 | Formally, composition and division fallacies occur in mereology [Hanna] |
| Full Idea: Informal fallacies of composition and division go over into formal fallacies of mereological logic. | |
| From: Robert Hanna (Rationality and Logic [2006], 7.3) |
| 9139 | If nothing exists, no truthmakers could make 'Nothing exists' true [Sorensen] |
| Full Idea: If nothing exists, then there are no truthmakers that could make 'Nothing exists' true. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 11.2) | |
| A reaction: [He cites David Lewis] We may be confusing truth with facts. I take facts to be independent of minds, but truth only makes sense as a concept in the presence of minds which are endeavouring to think well. |
| 9140 | Which toothbrush is the truthmaker for 'buy one, get one free'? [Sorensen] |
| Full Idea: If I buy two toothbrushes on a 'buy one, get one free' offer, which one did I buy and which one did I get free? Those who believe that each contingent truth has a truthmaker are forced to believe that 'buy one, get one free' is false. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 11.6) | |
| A reaction: Nice. There really is no fact of which toothbrush is the free one. The underlying proposition must presumably be 'two for the price of one'. But you could hardly fault the first slogan under the Trades Descriptions Act. |
| 11058 | Logic is explanatorily and ontologically dependent on rational animals [Hanna] |
| Full Idea: Logic is explanatorily and ontologically dependent on rational animals. | |
| From: Robert Hanna (Rationality and Logic [2006], 1.6) | |
| A reaction: This is a splendid defiance of the standard Fregean view of logic as having an inner validity of its own, having nothing to do with the psychology of thinkers. But if Hanna is right, why does logical consequence seem to be necessary? |
| 11072 | Logic is personal and variable, but it has a universal core [Hanna] |
| Full Idea: Beyond an innate and thus universally share protologic, each reasoner's mental logic is only more or less similar to the mental logic of any other reasoner. | |
| From: Robert Hanna (Rationality and Logic [2006], 5.7) | |
| A reaction: This is the main thesis of Hanna's book. I like the combination of this idea with Stephen Read's remark that each student should work out a personal logic which has their own private endorsement. |
| 11061 | Intensional consequence is based on the content of the concepts [Hanna] |
| Full Idea: In intensional logic the consequence relation is based on the form or content of the concepts or properties expressed by the predicates. | |
| From: Robert Hanna (Rationality and Logic [2006], 2.2) |
| 9119 | No attempt to deny bivalence has ever been accepted [Sorensen] |
| Full Idea: The history of deviant logics is without a single success. Bivalence has been denied at least since Aristotle, yet no anti-bivalent theory has ever left the philosophical nursery. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], Intro) | |
| A reaction: This is part of a claim that nothing in reality is vague - it is just our ignorance of the truth or falsity of some propositions. Personally I don't see why 'Grandad is bald' has to have a determinate truth value. |
| 9135 | We now see that generalizations use variables rather than abstract entities [Sorensen] |
| Full Idea: As philosophers gradually freed themselves from the assumption that all words are names, ..they realised that generalizations really use variables rather than names of abstract entities. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 8.4) | |
| A reaction: This looks like a key thought in trying to understand abstraction - though I don't think you can shake it off that easily. (For all x)(x-is-a-bird then x-has-wings) seems to require a generalised concept of a bird to give a value to the variable. |
| 9125 | Denying problems, or being romantically defeated by them, won't make them go away [Sorensen] |
| Full Idea: An unsolvable problem is still a problem, despite Wittgenstein's view that there are no genuine philosophical problems, and Kant's romantic defeatism in his treatment of the antinomies of pure reason. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 4.3) | |
| A reaction: I like the spin put on Kant, that he is a romantic in his defeatism. He certainly seems reluctant to slash at the Gordian knot, e.g. by being a bit more drastically sceptical about free will. |
| 21554 | Sets always exceed terms, so all the sets must exceed all the sets [Lackey] |
| Full Idea: Cantor proved that the number of sets in a collection of terms is larger than the number of terms. Hence Cantor's Paradox says the number of sets in the collection of all sets must be larger than the number of sets in the collection of all sets. | |
| From: Douglas Lackey (Intros to Russell's 'Essays in Analysis' [1973], p.127) | |
| A reaction: The sets must count as terms in the next iteration, but that is a normal application of the Power Set axiom. |
| 21553 | It seems that the ordinal number of all the ordinals must be bigger than itself [Lackey] |
| Full Idea: The ordinal series is well-ordered and thus has an ordinal number, and a series of ordinals to a given ordinal exceeds that ordinal by 1. So the series of all ordinals has an ordinal number that exceeds its own ordinal number by 1. | |
| From: Douglas Lackey (Intros to Russell's 'Essays in Analysis' [1973], p.127) | |
| A reaction: Formulated by Burali-Forti in 1897. |
| 9137 | Banning self-reference would outlaw 'This very sentence is in English' [Sorensen] |
| Full Idea: The old objection to the ban on self-reference is that it is too broad; it bans innocent sentences such as 'This very sentence is in English'. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 11.1) | |
| A reaction: Tricky. What is the sigificant difference between 'this sentence is in English' and 'this sentence is a lie'? The first concerns context and is partly metalinguistic. The second concerns semantics and truth. Concept and content.. |
| 11063 | Logicism struggles because there is no decent theory of analyticity [Hanna] |
| Full Idea: All versions of the thesis that arithmetic is reducible to logic remain questionable as long as no good theory of analyticity is available. | |
| From: Robert Hanna (Rationality and Logic [2006], 2.4) | |
| A reaction: He rejects the attempts by Frege, Wittgenstein and Carnap to provide a theory of analyticity. |
| 11055 | Supervenience can add covariation, upward dependence, and nomological connection [Hanna] |
| Full Idea: 'Strong supervenience' involves necessary covariation of the properties, and upward dependence of higher level on lower level. ...If we add a nomological connection between the two, then we have 'superdupervenience'. | |
| From: Robert Hanna (Rationality and Logic [2006], 1.2) | |
| A reaction: [compressed] Very helpful. A superdupervenient relationship between mind and brain would be rather baffling if they were not essentially the same thing. (which is what I take them to be). |
| 9116 | Vague words have hidden boundaries [Sorensen] |
| Full Idea: Vague words have hidden boundaries. The subtraction of a single grain of sand might turn a heap into a non-heap. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], Intro) | |
| A reaction: The first sentence could be the slogan for the epistemic view of vagueness. The opposite view is Sainsbury's - that vague words are those which do not have any boundaries. Sorensen admits his view is highly counterintuitive. I think I prefer Sainsbury. |
| 9132 | An offer of 'free coffee or juice' could slowly shift from exclusive 'or' to inclusive 'or' [Sorensen] |
| Full Idea: Sometimes an exclusive 'or' gradually develops into an inclusive 'or'. A restaurant offers 'free coffee or juice'. The customers ask for both, and gradually they are given it, first as a courtesy, and eventually as an expectation. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 7.2) | |
| A reaction: [compressed] A very nice example - of the rot of vagueness even seeping into the basic logical connectives. We don't have to accept it, though. Each instance of usage of 'or', by manager or customer, might be clearly one or the other. |
| 11083 | A sentence is necessary if it is true in a set of worlds, and nonfalse in the other worlds [Hanna] |
| Full Idea: On my view, necessity is the truth of a sentence in every member of a set of possible worlds, together with its nonfalsity in every other possible worlds. | |
| From: Robert Hanna (Rationality and Logic [2006], 6.6) |
| 11086 | Metaphysical necessity can be 'weak' (same as logical) and 'strong' (based on essences) [Hanna] |
| Full Idea: Weak metaphysical necessity is either over the set of all logically possible worlds (in which case it is the same as logical necessity), or it is of a smaller set of worlds, and is determined by the underlying essence or nature of the actual world. | |
| From: Robert Hanna (Rationality and Logic [2006], 6.6) | |
| A reaction: I take the first to be of no interest, as I have no interest in a world which is somehow rated as logically possible, but is not naturally possible. The second type should the principle aim of all human cognitive enquiry. The strong version is synthetic. |
| 11084 | Logical necessity is truth in all logically possible worlds, because of laws and concepts [Hanna] |
| Full Idea: Logical necessity is the truth of a sentence by virtue of logical laws or intrinsic conceptual connections alone, and thus true in all logically possible worlds. Put in traditional terms, logical necessity is analyticity. | |
| From: Robert Hanna (Rationality and Logic [2006], 6.6) |
| 11085 | Nomological necessity is truth in all logically possible worlds with our laws [Hanna] |
| Full Idea: Physical or nomological necessity is the truth of a sentence in all logically possible worlds governed by our actual laws of nature. | |
| From: Robert Hanna (Rationality and Logic [2006], 6.6) | |
| A reaction: Personally I think 'natural necessity' is the best label for this, as it avoids firm commitment to reductive physicalism, and it also avoids commitment to actual necessitating laws. |
| 9128 | It is propositional attitudes which can be a priori, not the propositions themselves [Sorensen] |
| Full Idea: The primary bearer of apriority is the propositional attitude (believing, knowing, guessing and so on) rather than the proposition itself. A proposition could be a priori to homo sapiens but a posteriori to Neandethals. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 6.3) | |
| A reaction: A putative supreme being is quite useful here, who might even see the necessity of Arsenal beating Manchester United next Saturday. Unlike infants, adults know a priori that square pegs won't fit round holes. |
| 9130 | Attributing apriority to a proposition is attributing a cognitive ability to someone [Sorensen] |
| Full Idea: Every attribution of apriority to a proposition is tacitly an attribution of a cognitive ability to some thinker. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 6.3) | |
| A reaction: The ability would include a range of background knowledge, as well as a sheer power of intellect. If you know all of Euclid's theorems, you will spot facts about geometrical figues quicker than me. His point is important. |
| 9118 | The colour bands of the spectrum arise from our biology; they do not exist in the physics [Sorensen] |
| Full Idea: The bands of colour in a colour spectrum do not correspond to objective discontinuities in light wavelengths. These apparently external bands arise from our biology rather than simple physics. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], Intro) | |
| A reaction: If any more arguments are needed to endorse the fact that some qualities are clearly secondary (and, to my amazement, such arguments seem to be very much needed), I would take this to be one of the final conclusive pieces of evidence. |
| 9124 | We are unable to perceive a nose (on the back of a mask) as concave [Sorensen] |
| Full Idea: The human perceptual system appears unable to represent a nose as concave rather than convex. If you look at the concave side of a mask, you see the features as convex. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 4.3) | |
| A reaction: I don't think that is quite true. You wouldn't put a mask on if you thought it was convex. It is usually when seen at a distance with strong cross-lighting that the effect emerges. Nevertheless, it is an important point. |
| 11077 | Intuition includes apriority, clarity, modality, authority, fallibility and no inferences [Hanna] |
| Full Idea: The nine features of intuition are: a mental act, apriority, content-comprehensiveness, clarity and distinctness, strict-modality-attributivity, authoritativeness,noninferentiality, cognitive indispensability, and fallibility. | |
| From: Robert Hanna (Rationality and Logic [2006], 6.4) | |
| A reaction: [See Hanna for a full explanation of this lot] Seems like a good stab at it. Note the trade-off between authority and fallibility. |
| 11080 | Intuition is more like memory, imagination or understanding, than like perception [Hanna] |
| Full Idea: There is no reason why intuition should be cognitively analogous not to sense perception but instead to either memory, imagination, or conceptual understanding. | |
| From: Robert Hanna (Rationality and Logic [2006], 6.5) | |
| A reaction: It is Russell's spotting the analogy with memory that made me come to believe that a priori knowledge is possible, as long as we accept it as being fallible. [Hanna has a good discussion of intuition; he votes for the imagination analogy] |
| 11078 | Intuition is only outside the 'space of reasons' if all reasons are inferential [Hanna] |
| Full Idea: Intuition is outside the 'space of reasons' if we assume that all reasons are inferential, but inside if we assume that reasons need not always be inferential. | |
| From: Robert Hanna (Rationality and Logic [2006], 6.4) | |
| A reaction: I take it that intuition can be firmly inside the space of reasons, and that not all reasons are inferential. |
| 9126 | Bayesians build near-certainty from lots of reasonably probable beliefs [Sorensen] |
| Full Idea: Bayesians demonstrate that a self-correcting agent can build an imposing edifice of near-certain knowledge from numerous beliefs that are only slightly more probable than not. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 6.1) | |
| A reaction: This strikes me as highly significant for the coherence account of justification, even if one is sceptical about the arithmetical approach to belief of Bayesianism. It seems obvious that lots of quite likely facts build towards certainty, Watson. |
| 9121 | Illusions are not a reason for skepticism, but a source of interesting scientific information [Sorensen] |
| Full Idea: Philosophers tend to associate illusions with skepticism. But since illusions are signs of modular construction, they are actually reason for scientific hope. Illusions have been very useful in helping us to understand vision. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 1.4) | |
| A reaction: This is a nice reversal of the usual view. If I see double, it reveals to me that my eyes are not aligned properly. Anyone led to scepticism by illusions should pay more attention to themselves, and less to the reality they hope to know directly. |
| 11053 | Explanatory reduction is stronger than ontological reduction [Hanna] |
| Full Idea: As standardly construed, reduction can be either explanatory or ontological. Explanatory reduction is the strongest sort of reduction. ...Ontological reduction can still have an 'explanatory gap'. | |
| From: Robert Hanna (Rationality and Logic [2006], 1.1) |
| 11081 | Imagination grasps abstracta, generates images, and has its own correctness conditions [Hanna] |
| Full Idea: Three features of imagination are that its objects can be abstract, that it generates spatial images directly available to introspection, and its correctness conditions are not based on either efficacious causation or effective tracking. | |
| From: Robert Hanna (Rationality and Logic [2006], 6.6) | |
| A reaction: Hanna makes the imagination faculty central to our grasp of his proto-logic. |
| 11082 | Should we take the 'depictivist' or the 'descriptivist/propositionalist' view of mental imagery? [Hanna] |
| Full Idea: In the debate in cognitive science on the nature of mental imagery, there is a 'depictivist' side (Johnson-Laird, Kosslyn, Shepard - good images are isomorphic), and a 'descriptivist' or 'propositionalist' side (Pylyshyn and others). | |
| From: Robert Hanna (Rationality and Logic [2006], 6.6) | |
| A reaction: Hanna votes firmly in favour of the first view, and implies that they have more or less won the debate. |
| 11047 | Hegelian holistic rationality is the capacity to seek coherence [Hanna] |
| Full Idea: The 'holistic' (Hegelian) sense of rationality means the capacity for systematically seeking coherence (or 'reflective equilibrium') across a network or web of beliefs, desires, emotions, intentions and volitions. Traditionally 'the truth is the whole'. | |
| From: Robert Hanna (Rationality and Logic [2006], Intro) | |
| A reaction: On the whole this is my preferred view (which sounds Quinean as well as Hegelian), though I reject the notion that truth is a whole. I take coherence to be the hallmark of justification, though not of truth, and reason aims to justify. |
| 11048 | Humean Instrumental rationality is the capacity to seek contingent truths [Hanna] |
| Full Idea: The 'instrumental' (Humean) sense of rationality means a capacity for generating or recognizing contingent truths, contextually normative rules, consequentialist obligations, and hypothetical 'ought' claims. Reason is 'the slave of the passions'. | |
| From: Robert Hanna (Rationality and Logic [2006], Intro) |
| 11046 | Kantian principled rationality is recognition of a priori universal truths [Hanna] |
| Full Idea: The 'principled' (Kantian) sense of rationality means the possession of a capacity for generating or recognizing necessary truths, a priori beliefs, strictly universal normative rules, nonconsequentialist moral obligations, and categorical 'ought' claims. | |
| From: Robert Hanna (Rationality and Logic [2006], Intro) |
| 11067 | Rational animals have a normative concept of necessity [Hanna] |
| Full Idea: A rational animal is one that is a normative-reflective possessor of the concepts of necessity, certainty and unconditional obligation. | |
| From: Robert Hanna (Rationality and Logic [2006], 4.0) | |
| A reaction: The addition of obligation shows the Kantian roots of this. It isn't enough just to possess a few concepts. You wouldn't count as rational if you didn't desire truth, as well as understanding it. Robots be warned. |
| 11068 | One tradition says talking is the essence of rationality; the other says the essence is logic [Hanna] |
| Full Idea: In the tradition of Descartes, Chomsky and Davidson, rational animals are essentially talking animals. But in the view of Kant, and perhaps Fodor, it is the cognitive capacity for logic that is the essence of human rationality. | |
| From: Robert Hanna (Rationality and Logic [2006], 4.9) |
| 11045 | Most psychologists are now cognitivists [Hanna] |
| Full Idea: Most psychologists have now dropped behaviourism and adopted cognitivism: the thesis that the rational human mind is essentially an active innately specified information-processor. | |
| From: Robert Hanna (Rationality and Logic [2006], Intro) |
| 9134 | The negation of a meaningful sentence must itself be meaningful [Sorensen] |
| Full Idea: The negation of any meaningful sentence must itself be meaningful. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 8.1) | |
| A reaction: Nice. Compare 'there is another prime number beyond the highest one we have found' with its negation. The first seems verifiable in principle, but the second one doesn't. So the verificationist must deny Sorensen's idea? |
| 9133 | Propositions are what settle problems of ambiguity in sentences [Sorensen] |
| Full Idea: Propositions play the role of dis-ambiguators; they are the things between which utterances are ambiguous. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 7.7) | |
| A reaction: I have become a great fan of propositions, and I think this is one of the key reasons for believing in them. The proposition is what we attempt to pin down when asked 'what exactly did you mean by what you just said?' |
| 9129 | I can buy any litre of water, but not every litre of water [Sorensen] |
| Full Idea: I am entitled to buy any litre of water, but I am not entitled to buy every litre of water. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 6.3) | |
| A reaction: A decent social system must somehow draw a line between buying up all the water and buying up all the paintings of Vermeer. Even the latter seems wicked, but it is hard to pin down the reason. |
| 9122 | God cannot experience unwanted pain, so God cannot understand human beings [Sorensen] |
| Full Idea: Theologians worry that God may be an alien being. God cannot feel pain since pain is endured against one's will. God is all powerful and suffers nothing against His Will. To understand pain, one must experience pain. So God's power walls him off from us. | |
| From: Roy Sorensen (Vagueness and Contradiction [2001], 3.2) | |
| A reaction: I can't think of a good theological reply to this. God, and Jesus too (presumably), can only experience pain if they volunteer for it. It is inconceivable that they could be desperate for it to stop, but were unable to achieve that. |