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! |
| 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. |
| 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. |
| 23681 | The first motion or effect cannot be produced necessarily, so the First Cause must be a free agent [Reid] |
| Full Idea: That the first motion, or the first effect, whatever it be, cannot be produced necessarily, and, consequently, that the First Cause must be a free agent, has been demonstrated clearly and unanswerably. | |
| From: Thomas Reid (Essays on Active Powers 4: Liberty of Agents [1788], 8) | |
| A reaction: He has said that the First Cause can only be conceived by us as an 'agent'. If there is an agential First Cause, then he must be right. It is this need for God to be free which makes scepticism about free will unacceptable to many. |
| 23676 | A willed action needs reasonable understanding of what is to be done [Reid] |
| Full Idea: There can be no will without such a degree of understanding, at least, as gives the conception of that which we will. | |
| From: Thomas Reid (Essays on Active Powers 4: Liberty of Agents [1788], 1) | |
| A reaction: Presumably this 'conception' includes an understanding of the probable consequences, but they are of infinite complexity. I see this as an objection to 'ultimate' free will and responsibility, because there are only ever degrees of understanding. |
| 23680 | We are morally free, because we experience it, we are accountable, and we pursue projects [Reid] |
| Full Idea: I believe in moral liberty first because we have a natural conviction of belief that in many cases we act freely, second because we are accountable, and third because we can prosecute an end by a long series of means adapted. | |
| From: Thomas Reid (Essays on Active Powers 4: Liberty of Agents [1788], 5) | |
| A reaction: This is his final summary of why he believes in free will. Why didn't Plato and Aristotle have this natural belief? He could only believe we are 'accountable' because he believes in free will. Ants and bees pursue lengthy projects. Hm. |
| 23996 | Akrasia is intelligible in hindsight, when we revisit our previous emotions [Blackburn] |
| Full Idea: To make my emotion intelligible [in a weakness of will case] is to look back and recognise that my emotions and dispositions were not quite as I had taken them to be. It is quite useless in such a case to invoke a blanket diagnosis of 'irrationality'. | |
| From: Simon Blackburn (Ruling Passions [1998], p.191) | |
| A reaction: So Blackburn rejects the idea of akrasia, because there was never really a conflict. He says rational people always aim to maximise their utility (p.135), and if their own act surprises them, it is just a failure to understand their own rationality. |
| 23678 | A motive is merely an idea, like advice, and not a force for action [Reid] |
| Full Idea: A motive is equally incapable of action and of passion; because it is not a thing that exists, but a thing that is conceived. …Motives may be compared to advice or exhortation. | |
| From: Thomas Reid (Essays on Active Powers 4: Liberty of Agents [1788], 4) | |
| A reaction: We say people are motivated by greed or anger or love, which seems a bit stronger than mere advice. |
| 23677 | We all know that mere priority or constant conjunction do not have to imply causation [Reid] |
| Full Idea: Every man who understands the language knows that neither priority, nor constant conjunction, nor both taken together, imply efficiency. | |
| From: Thomas Reid (Essays on Active Powers 4: Liberty of Agents [1788], 2) | |
| A reaction: This invites the question of how we do know causal events, if none of our experiences are enough to prove it. Reid says we have an innate knowledge that all events are caused, but that isn't much help. The presence of power? |
| 23679 | The principle of the law of nature is that matter is passive, and is acted upon [Reid] |
| Full Idea: The law of nature respecting matter is grounded upon this principle: That matter is an inert, inactive substance, which does not act, but is acted upon. | |
| From: Thomas Reid (Essays on Active Powers 4: Liberty of Agents [1788], 5) | |
| A reaction: A clear statement (alongside Euler's) of the 18th century view, still with us, but strikes me as entirely wrong. Their view needs the active power of God to drive the laws. Matter has intrinsic primitive powers, and laws describe patterns of behaviour. |