17 ideas
| 8952 | We reach 'reflective equilibrium' when intuitions and theory completely align [Fisher] |
| Full Idea: A state of 'reflective equilibrium' is when our theory and our intuitions become completely aligned | |
| From: Jennifer Fisher (On the Philosophy of Logic [2008], 12.IV) | |
| A reaction: [Rawls made this concept famous] This is a helpful concept in trying to spell out the ideal which is the dream of believers in 'pure reason' - that there is a goal in which everything comes right. The problem is when people have different intuitions! |
| 13591 | Quantified modal logic collapses if essence is withdrawn [Quine] |
| Full Idea: The whole of quantified modal logic collapses if essence is withdrawn. | |
| From: Willard Quine (Intensions Revisited [1977], p.121) | |
| A reaction: Quine offers an interesting qualification to this crushing remark in Idea 13590. The point is that objects must retain their identity in modal contexts, as if I say 'John Kennedy might have been Richard Nixon'. What could that mean? |
| 8943 | Three-valued logic says excluded middle and non-contradition are not tautologies [Fisher] |
| Full Idea: In three-valued logic (L3), neither the law of excluded middle (p or not-p), nor the law of non-contradiction (not(p and not-p)) will be tautologies. If p has the value 'indeterminate' then so will not-p. | |
| From: Jennifer Fisher (On the Philosophy of Logic [2008], 07.I) | |
| A reaction: I quite accept that the world is full of indeterminate propositions, and that excluded middle and non-contradiction can sometimes be uncertain, but I am reluctant to accept that what is being offered here should be called 'logic'. |
| 8945 | Fuzzy logic has many truth values, ranging in fractions from 0 to 1 [Fisher] |
| Full Idea: In fuzzy logic objects have properties to a greater or lesser degree, and truth values are given as fractions or decimals, ranging from 0 to 1. Not-p is defined as 1-p, and other formula are defined in terms of maxima and minima for sets. | |
| From: Jennifer Fisher (On the Philosophy of Logic [2008], 07.II) | |
| A reaction: The question seems to be whether this is actually logic, or a recasting of probability theory. Susan Haack attacks it. If logic is the study of how truth is preserved as we move between propositions, then 0 and 1 need a special status. |
| 8951 | Classical logic is: excluded middle, non-contradiction, contradictions imply all, disjunctive syllogism [Fisher] |
| Full Idea: For simplicity, we can say that 'classical logic' amounts to the truth of four sentences: 1) either p or not-p; 2) it is not the case that both p and not-p; 3) from p and not-p, infer q; 4) from p or q and not-p, infer q. | |
| From: Jennifer Fisher (On the Philosophy of Logic [2008], 12.I) | |
| A reaction: [She says there are many ways of specifying classical logic] Intuition suggests that 2 and 4 are rather hard to dispute, while 1 is ignoring some grey areas, and 3 is totally ridiculous. There is, of course, plenty of support for 3! |
| 8950 | Logic formalizes how we should reason, but it shouldn't determine whether we are realists [Fisher] |
| Full Idea: Even if one is inclined to be a realist about everything, it is hard to see why our logic should be the determiner. Logic is supposed to formalize how we ought to reason, but whether or not we should be realists is a matter of philosophy, not logic. | |
| From: Jennifer Fisher (On the Philosophy of Logic [2008], 09.I) | |
| A reaction: Nice to hear a logician saying this. I do not see why talk in terms of an object is a commitment to its existence. We can discuss the philosopher's stone, or Arthur's sword, or the Loch Ness monster, or gravitinos, with degrees of commitment. |
| 8946 | We could make our intuitions about heaps precise with a million-valued logic [Fisher] |
| Full Idea: We could construct a 1,000,000-valued logic that would allow our intuitions concerning a heap to vary exactly with the amount of sand in the heap. | |
| From: Jennifer Fisher (On the Philosophy of Logic [2008]) | |
| A reaction: Presumably only an infinite number of grains of sand would then produce a true heap, and even one grain would count as a bit of a heap, which must both be wrong, so I can't see this helping much. |
| 8944 | Vagueness can involve components (like baldness), or not (like boredom) [Fisher] |
| Full Idea: Vague terms come in at least two different kinds: those whose constituent parts come in discrete packets (bald, rich, red) and those that don't (beauty, boredom, niceness). | |
| From: Jennifer Fisher (On the Philosophy of Logic [2008], 07.II) | |
| A reaction: The first group seem to be features of the external world, and the second all occur in the mind. Baldness may be vague, but presumably hairs are (on the whole) not. Nature doesn't care whether someone is actually 'bald' or not. |
| 13590 | Essences can make sense in a particular context or enquiry, as the most basic predicates [Quine] |
| Full Idea: The notion of essence makes sense in context. Relative to a particular enquiry, some predicates may play a more basic role than others, or may apply more fixedly; and these may be treated as essential. | |
| From: Willard Quine (Intensions Revisited [1977], p.121) | |
| A reaction: Quine has got a bad press on essentialism, and on modal logic, but I take this point seriously. If you give something a fixed identity by means of essence in some context, you can then go ahead and apply possible world reasoning in that context. |
| 8483 | Necessity is relative to context; it is what is assumed in an inquiry [Quine] |
| Full Idea: The very notion of necessity makes sense to me only relative to context. Typically it is applied to what is assumed in an inquiry, as against what has yet to transpire. | |
| From: Willard Quine (Intensions Revisited [1977], p.121) | |
| A reaction: Lots of things are assumed by an inquiry without an assumption that they must be true. Quine is the greatest opponent of necessity in all of philosophy. Asserting necessities, though, is too much fun to give up. It would ruin philosophy. |
| 8941 | We can't explain 'possibility' in terms of 'possible' worlds [Fisher] |
| Full Idea: Explaining 'it is possible that p' by saying p is true in at least one possible world doesn't get me very far. If I don't understand what possibility is, then appealing to possible worlds is not going to do me much good. | |
| From: Jennifer Fisher (On the Philosophy of Logic [2008], 06.III) | |
| A reaction: This seems so blatant that I assume friends of possible worlds will have addressed the problem. Note that you will also need to understand 'possible' to define necessity as 'true in all possible worlds'. Necessarily-p is not-possibly-not-p. |
| 8947 | If all truths are implied by a falsehood, then not-p might imply both q and not-q [Fisher] |
| Full Idea: If all truths are implied by a falsehood, then 'if there are no trees in the park then there is no shade' and 'if there are no trees in the park there is plenty of shade' both come out as true. Intuitively, though, the second one is false. | |
| From: Jennifer Fisher (On the Philosophy of Logic [2008], 08.I) | |
| A reaction: The rule that a falsehood implies all truths must be the weakest idea in classical logic, if it actually implies a contradiction. This means we must take an interest in relevance logics. |
| 8949 | In relevance logic, conditionals help information to flow from antecedent to consequent [Fisher] |
| Full Idea: A good account of relevance logic suggests that a conditional will be true when the flow of information is such that a conditional is the device that helps information to flow from the antecedent to the consequent. | |
| From: Jennifer Fisher (On the Philosophy of Logic [2008], 08.III) | |
| A reaction: Hm. 'If you are going out, you'll need an umbrella'. This passes on information about 'out', but also brings in new information. 'If you are going out, I'm leaving you'. What flows is an interpretation of the antecedent. Tricky. |
| 13589 | Possible worlds are a way to dramatise essentialism, and yet they presuppose essentialism [Quine] |
| Full Idea: Talk of possible worlds is a graphic way of waging the essentialist philosophy, but it is only that; it is not an explication. Essence is needed to identify an object from one possible world to another. | |
| From: Willard Quine (Intensions Revisited [1977], p.118) | |
| A reaction: He makes the proposal sound circular, but I take a commitment to essences to be prior to talk of possible worlds. Possible worlds are a tool for clarifying modalities, not for clarifying essential identities. |
| 13588 | A rigid designator (for all possible worlds) picks out an object by its essential traits [Quine] |
| Full Idea: A rigid designator differs from others in that it picks out its object by essential traits. It designates the object in all possible worlds in which it exists. | |
| From: Willard Quine (Intensions Revisited [1977], p.118) | |
| A reaction: This states the point more clearly than Kripke ever does, and I presume it is right. Thus when we say that we wish 'our' Hubert Humphrey had won the election, we can allow that his victory elation would change him a bit. Kripke is right. |
| 13592 | Beliefs can be ascribed to machines [Quine] |
| Full Idea: Beliefs have been ascribed to machines, in support of a mechanistic philosophy, and I share this attitude. | |
| From: Willard Quine (Intensions Revisited [1977], p.123) | |
| A reaction: [He cites Raymond Nelson] One suspects that this is Quine's latent behaviourism speaking. It strikes me as a crass misuse of 'belief' to ascribe it to a simple machine like a thermostat. |
| 22450 | If moral systems can't judge other moral systems, then moral relativism is true [Williams,B, by Foot] |
| Full Idea: If some societies with divergent moral systems merely confront each other, having no use for the assertion that their own systems are true and the others false except to mark the system to which they adhere, then relativism is a true theory of morality. | |
| From: report of Bernard Williams (The Truth in Relativism [1974]) by Philippa Foot - Moral Relativism p.3 | |
| A reaction: 'Having no use for' an assertion is not the same as the assertion being impossible. Some liberal cultures refuse to criticise others because their highest value is tolerance, even when the target culture wholly contradicts the critics' other values. |