26 ideas
| 19066 | Philosophy aims to understand the world, through ordinary experience and science [Dummett] |
| Full Idea: Philosophy is an attempt to understand the world, as it is revealed to us both in our ordinary experience and by the discoveries and theories of science. | |
| From: Michael Dummett (The Justification of Deduction [1973], p.311) | |
| A reaction: I don't see a sharp division between 'ordinary' and 'scientific'. I really like this idea, first because it makes 'understanding' central, and second because it wants both revelations. In discussing matter and time, there is too much emphasis on science. |
| 13070 | If definitions must be general, and general terms can't individuate, then Socrates can't be defined [Aquinas, by Cover/O'Leary-Hawthorne] |
| Full Idea: Socrates has no definition if definitions by their nature must be in purely general terms, and if no purely general terms can succeed in uniquely singling out this signated matter. | |
| From: report of Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], 23) by Cover,J/O'Leary-Hawthorne,J - Substance and Individuation in Leibniz 1.1.2 | |
| A reaction: There seem to be two models. That general terms actually individuate the matter of Socrates, or that they cross-reference to (so to speak) define Socrates 'by elimination', as the only individual that fits. But the latter is a poor definition. |
| 11197 | The definitions expressing identity are used to sort things [Aquinas] |
| Full Idea: What sorts things into their proper genus and species are the definitions that express what they are. | |
| From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.92) | |
| A reaction: This is straight from Aristotle, though Aristotle's view is a little more complex, I think. If the definitions 'express what they are', then definitions seem to specify the essence. |
| 19067 | A successful proof requires recognition of truth at every step [Dummett] |
| Full Idea: For a demonstration to be cogent it is necessary that the passage from step to step involve a recognition of truth at each line. | |
| From: Michael Dummett (The Justification of Deduction [1973], p.313) | |
| A reaction: Dummett cited Quine (esp. 1970) as having an almost entirely syntactic view of logic. Rumfitt points out that logic can move validly from one falsehood to another. Even a 'proof' might detour into falsehood, but it would not be a 'canonical' proof! |
| 19060 | Truth-tables are dubious in some cases, and may be a bad way to explain connective meaning [Dummett] |
| Full Idea: It is arguable whether two-valued truth tables give correct meanings for certain sentential operators, and even whether they constitute legitimate explanations of any possible sentential operators. | |
| From: Michael Dummett (The Justification of Deduction [1973], p.294) | |
| A reaction: See 'Many-valued logic' for examples of non-binary truth tables. Presumably logicians should aspire to make their semantics precise, as well as their syntax. |
| 11066 | Deduction is justified by the semantics of its metalanguage [Dummett, by Hanna] |
| Full Idea: For Dummett the semantics of the metalanguage is the external and objective source of the justification of deduction. | |
| From: report of Michael Dummett (The Justification of Deduction [1973]) by Robert Hanna - Rationality and Logic 3.4 | |
| A reaction: This is offered as an answer to the Lewis Carroll problem that justifying deduction seems to need deduction, thus leading to a regress. [There is a reply to Dummett by Susan Haack] |
| 19058 | Syntactic consequence is positive, for validity; semantic version is negative, with counterexamples [Dummett] |
| Full Idea: A plausible account is that the syntactic notion of consequence is for positive results, that some form of argument is valid; the semantic notion is required for negative results, that some argument is invalid, because a counterexample can be found. | |
| From: Michael Dummett (The Justification of Deduction [1973], p.292) | |
| A reaction: This rings true for the two strategies of demonstration, the first by following the rules in steps, the second by using your imagination (or a tableau) to think up problems. |
| 19063 | Beth trees show semantics for intuitionistic logic, in terms of how truth has been established [Dummett] |
| Full Idea: Beth trees give a semantics for intuitionistic logic, by representing sentence meaning in terms of conditions under which it is recognised to have been established as true. | |
| From: Michael Dummett (The Justification of Deduction [1973], p.305) |
| 19059 | In standard views you could replace 'true' and 'false' with mere 0 and 1 [Dummett] |
| Full Idea: Nothing is lost, on this view, if in the standard semantic treatment of classical sentential logic, we replace the standard truth-values 'true' and 'false' by the numbers 0 and 1. | |
| From: Michael Dummett (The Justification of Deduction [1973], p.294) | |
| A reaction: [A long context will explain 'on this view'] He is discussing the relationship of syntactic and semantic consequence, and goes on to criticise simple binary truth-table accounts of connectives. Semantics on a computer would just be 0 and 1. |
| 19062 | Classical two-valued semantics implies that meaning is grasped through truth-conditions [Dummett] |
| Full Idea: The standard two-valued semantics for classical logic involves a conception under which to grasp the meaning of a sentence is to apprehend the conditions under which it is, or is not, true. | |
| From: Michael Dummett (The Justification of Deduction [1973], p.305) | |
| A reaction: The idea is that you only have to grasp the truth tables for sentential logic, and that needs nothing more than knowing whether a sentence is true or false. I'm not sure where the 'conditions' creep in, though. |
| 19065 | Soundness and completeness proofs test the theory of meaning, rather than the logic theory [Dummett] |
| Full Idea: A proof of soundess or completeness is a test, not so much of the logical theory to which it applies, but of the theory of meaning which underlies the semantics. | |
| From: Michael Dummett (The Justification of Deduction [1973], p.310) | |
| A reaction: These two types of proof concern how the syntax and the semantics match up, so this claim sounds plausible, though I tend to think of them as more like roadworthiness tests for logic, checking how well they function. |
| 11195 | If affirmative propositions express being, we affirm about what is absent [Aquinas] |
| Full Idea: If being is what makes propositions true, then anything we can express in an affirmative proposition, however unreal, is said to be; so lacks and absences are, since we say that absences are opposed to presences, and blindness exists in an eye. | |
| From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.92) | |
| A reaction: See Idea 11194 for the alternative Aristotelian approach to being, according to categories. Do absences and lacks have real essences, or causal properties? The absence of the sentry may cause the loss of the city. |
| 11201 | Properties have an incomplete essence, with definitions referring to their subject [Aquinas] |
| Full Idea: Incidental properties have an incomplete essence, and need to refer in their definitions to their subject, lying outside their own genus. | |
| From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.93) | |
| A reaction: These are 'incidental' properties, but it is a nice question whether properties have essences. Presumably they must have if they are universals, or platonic Forms. The notion of being 'strong' can be defined without specific examples. |
| 11205 | If the form of 'human' contains 'many', Socrates isn't human; if it contains 'one', Socrates is Plato [Aquinas] |
| Full Idea: If (in the Platonic view) manyness was contained in humanness it could never be one as it is in Socrates, and if oneness was part of its definition then Socrates would be Plato and the nature couldn't be realised more than once. | |
| From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.100) | |
| A reaction: I suppose the reply is that since we are trying to explain one-over-many, then this unusual combination of both manyness and oneness is precisely what distinguishes forms from other ideas. |
| 13090 | The principle of diversity for corporeal substances is their matter [Aquinas, by Cover/O'Leary-Hawthorne] |
| Full Idea: In the view of Aquinas, while substantial form is the ultimate ground of identity and difference of angels, it is matter that provides a principle of diversity in the case of corporeal substances. | |
| From: report of Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267]) by Cover,J/O'Leary-Hawthorne,J - Substance and Individuation in Leibniz 5.2.3 | |
| A reaction: This is at least as good a proposal as their apatial location. There is more chance of reidentifying matter than of precisely reidentifying a spatial location. Two indistinguishable spheres remain the classic problem case (of Max Black, Idea 10195) |
| 11202 | It is by having essence that things exist [Aquinas] |
| Full Idea: It is by having essence that things exist. | |
| From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.94) | |
| A reaction: Compare Idea 11199, which gives a fuller picture. This idea seems to suggest essence as the cause of existence, which sounds wrong. Perhaps essence is a necessary condition of existence, but it is necessary that nothing indeterminate can exist? |
| 11203 | Specific individual essence is defined by material, and generic essence is defined by form [Aquinas] |
| Full Idea: Specific essence differs from generic essence by being demarcated: individuals are demarcated within species by dimensionally defined material, but species within genus by a defining differentiation taken from the form. | |
| From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.95) | |
| A reaction: It clearly won't be enough to define an individual just to define its material and its shape. The material might also be essential to the genus, as when defining fire. Probably not very helpful. |
| 11200 | The definition of a physical object must include the material as well as the form [Aquinas] |
| Full Idea: Form alone cannot be a composite substance's essence. For a thing's essence is expressed by its definition, and unless the definition of a physical substance included both form and material, the definition wouldn't differ from mathematical objects. | |
| From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.93) | |
| A reaction: This is the sort of thoroughly sensible remark that you only get from the greatest philosophers. Minor philosophers fall in love with things like forms, and then try to use them to explain everything. |
| 11196 | Essence is something in common between the natures which sort things into categories [Aquinas] |
| Full Idea: Since being as belonging to a category expresses the 'isness' of things, and belongs to all ten Aristotelian categories, essence must be something all the natures that sort different beings into genera and species have in common. | |
| From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.92) | |
| A reaction: I like this because it is the essence which does the sorting, not the sorting which defines the essence (which seems to me to be a deep and widespread confusion). |
| 11208 | A simple substance is its own essence [Aquinas] |
| Full Idea: A simple substance is its own essence. | |
| From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.103) | |
| A reaction: Aquinas takes complex substances to have their essences in various ways, but this thought is the basis of all essence. Presumably the Greek word 'ousia' names the key ingredient. |
| 18284 | Particulars can be verified or falsified, but general statements can only be falsified (conclusively) [Popper] |
| Full Idea: Whereas particular reality statements are in principle completely verifiable or falsifiable, things are different for general reality statements: they can indeed be conclusively falsified, they can acquire a negative truth value, but not a positive one. | |
| From: Karl Popper (Two Problems of Epistemology [1932], p.256), quoted by J. Alberto Coffa - The Semantic Tradition from Kant to Carnap 18 'Laws' | |
| A reaction: This sounds like a logician's approach to science, but I prefer to look at coherence, where very little is actually conclusive, and one tinkers with the theory instead. |
| 19061 | An explanation is often a deduction, but that may well beg the question [Dummett] |
| Full Idea: An explanation is often a deductive argument, with the fact needing explaining as its conclusion. ...But the conclusion is usually given in advance, and we may only believe the premisses because they plausibly explain the conclusion. | |
| From: Michael Dummett (The Justification of Deduction [1973], p.296) | |
| A reaction: [compressed (Dummett's wordy prose cries out for it!)] I suppose this works better in mathematics, which is central to Dummett's interests. In the real world the puzzle is not usually logically implied by its explanation. |
| 11198 | Definition of essence makes things understandable [Aquinas] |
| Full Idea: It is definition of essence that makes things understandable. | |
| From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.92) | |
| A reaction: The aim of philosophy is understanding, which is achieved by successful explanation. I totally agree with this Aristotelian view, so neatly summarised by Aquinas. |
| 19064 | Holism is not a theory of meaning; it is the denial that a theory of meaning is possible [Dummett] |
| Full Idea: In the sense of giving a model for the content of a sentence, its representative power, holism is not a theory of meaning; it is the denial that a theory of meaning is possible. | |
| From: Michael Dummett (The Justification of Deduction [1973], p.309) | |
| A reaction: This will obviously be because sentences just don't have meaning in isolation, so their meaning can't be given in terms of the sentences. |
| 11206 | The mind constructs complete attributions, based on the unified elements of the real world [Aquinas] |
| Full Idea: Attribution is something mind brings to completion by constructing propositional connections and disconnections, basing itself on real-world unity possessed by the things being attributed to one another. | |
| From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.102) | |
| A reaction: This compromise story seems to me to be exactly right. I take it that we respond to the real joints of nature, but using thought and language which is riddled with convention. |
| 11207 | A cause can exist without its effect, but the effect cannot exist without its cause [Aquinas] |
| Full Idea: When things are so related that one causes the other to exist, the cause can exist without what it causes but not vice versa. | |
| From: Thomas Aquinas (De Ente et Essentia (Being and Essence) [1267], p.103) | |
| A reaction: This is open to question, if causes are supposed to be sufficient for effects. Presumably Aquinas would support the view that if the cause had not been, the effect would not have happened. But the current idea indicates the priority relation. |