19 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. |
| 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. |
| 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. |
| 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. |
| 22465 | We see a moral distinction between doing and allowing to happen [Foot] |
| Full Idea: We have an intuition that there is a morally relevant distinction between what we do and what we allow to happen. | |
| From: Philippa Foot (Morality, Action, and Outcome [1985], p.88) | |
| A reaction: She says many deny this distinction, but she defends it. Presumably consequentialists deny the distinction. What is bad if I do it, but OK if I allow it to happen? Neglecting a victim to save others, she suggests. |
| 22466 | We see a moral distinction between our aims and their foreseen consequences [Foot] |
| Full Idea: We have an intuition that there is a moral distinction between what we aim at and what we foresee as a result of what we do. | |
| From: Philippa Foot (Morality, Action, and Outcome [1985], p.88) | |
| A reaction: Cf. Idea 22465. This seems to be the classic doctrine of double effect. It is hard to defend the claim that we are only responsible for what we aim at. A wide assessment of consequences is a moral duty. Well-meaning fools are bad. |
| 22467 | Acts and omissions only matter if they concern doing something versus allowing it [Foot] |
| Full Idea: The difference between acts and omissions is irrelevant to any moral issue except in so far as it corresponds to the distinction between allowing something to happen and being the agent to whom the happening can be ascribed. | |
| From: Philippa Foot (Morality, Action, and Outcome [1985], p.89) | |
| A reaction: The list of anyone's omissions is presumably infinite, but what they 'allow' must be in some way within their power. But what of something I can't now prevent, only because I failed to do some relevant task yesterday? |
| 22470 | A good moral system benefits its participants, and so demands reciprocity [Foot] |
| Full Idea: It has been suggested that one criterion for a good moral system is that it should be possible to demand reciprocity from every individual because of the good the system renders to him. | |
| From: Philippa Foot (Morality, Action, and Outcome [1985], p.104) | |
| A reaction: Money seems to have this feature, that we mostly conform to the rules for its use, because we value the whole system. Foot accepts this, but says there are also other criteria, such as leaving freedom to live well (ie. not too puritanical). |
| 22468 | Virtues can have aims, but good states of affairs are not among them [Foot] |
| Full Idea: Some virtues do give us aims, but nothing from within morality suggests the kind of good state of affairs which it would seem always to be our duty to promote. And why indeed should there be any such thing? | |
| From: Philippa Foot (Morality, Action, and Outcome [1985], p.101) | |
| A reaction: Isn't successful human functioning, such as heath, always to be desired? If honour is a worthy aim, doesn't that make being rightly honoured a desirable state of affairs? She is attacking consequentialism, but I'm not convinced here. |
| 22469 | Some virtues imply rules, and others concern attachment [Foot] |
| Full Idea: Virtues such as justice consist mainly in adherence to rules of conduct, while those such as benevolence we might call virtues of attachment. | |
| From: Philippa Foot (Morality, Action, and Outcome [1985], p.101) | |
| A reaction: Not sure about 'attachment'. We should be benevolent towards people to whom we are not particularly attached. Courage doesn't fall into either group. |
| 13304 | Learned men gain more in one day than others do in a lifetime [Posidonius] |
| Full Idea: In a single day there lies open to men of learning more than there ever does to the unenlightened in the longest of lifetimes. | |
| From: Posidonius (fragments/reports [c.95 BCE]), quoted by Seneca the Younger - Letters from a Stoic 078 | |
| A reaction: These remarks endorsing the infinite superiority of the educated to the uneducated seem to have been popular in late antiquity. It tends to be the religions which discourage great learning, especially in their emphasis on a single book. |
| 20820 | Time is an interval of motion, or the measure of speed [Posidonius, by Stobaeus] |
| Full Idea: Posidonius defined time thus: it is an interval of motion, or the measure of speed and slowness. | |
| From: report of Posidonius (fragments/reports [c.95 BCE]) by John Stobaeus - Anthology 1.08.42 | |
| A reaction: Hm. Can we define motion or speed without alluding to time? Looks like we have to define them as a conjoined pair, which means we cannot fully understand either of them. |