16 ideas
| 9390 | Logic guides thinking, but it isn't a substitute for it [Rumfitt] |
| Full Idea: Logic is part of a normative theory of thinking, not a substitute for thinking. | |
| From: Ian Rumfitt (The Logic of Boundaryless Concepts [2007], p.13) | |
| A reaction: There is some sort of logicians' dream, going back to Leibniz, of a reasoning engine, which accepts propositions and outputs inferences. I agree with this idea. People who excel at logic are often, it seems to me, modest at philosophy. |
| 9389 | Vague membership of sets is possible if the set is defined by its concept, not its members [Rumfitt] |
| Full Idea: Vagueness in respect of membership is consistency with determinacy of the set's identity, so long as a set's identity is taken to consist, not in its having such-and-such members, but in its being the extension of a concept. | |
| From: Ian Rumfitt (The Logic of Boundaryless Concepts [2007], p.5) | |
| A reaction: I find this view of sets much more appealing than the one that identifies a set with its members. The empty set is less of a problem, as well as non-existents. Logicians prefer the extensional view because it is tidy. |
| 19419 | Not all of perception is accompanied by consciousness [Leibniz] |
| Full Idea: I do not think that the Cartesians have ever proved or can prove that every perception is accompanied by consciousness. | |
| From: Gottfried Leibniz (Principle of Life and Plastic Natures [1705], p.195) | |
| A reaction: This idea is very important in Leibniz, because non-conscious or barely conscious thoughts and perceptions explain a huge amount about behaviour, reality and morality. |
| 19544 | Closure says if you know P, and also know P implies Q, then you must know Q [Dretske] |
| Full Idea: Closure is the epistemological principle that if S knows that P is true and knows that P implies Q, then, evidentially speaking, this is enough for S to know that Q is true. Nothing more is needed. | |
| From: Fred Dretske (The Case against Closure (and reply) [2005], p.25) | |
| A reaction: [Dretske was the first to raise this issue] It is 'closure' because it applies to every case of Q, which is every implication of P that is known. The issue is whether we really do know all such Qs. Dretske doubts it. See his zebra case. |
| 19545 | We needn't regret the implications of our regrets; regretting drinking too much implies the past is real [Dretske] |
| Full Idea: One doesn't have to regret everything one knows to be implied by what one regrets. Tom regrets drinking three martinis, but doesn't regret what he knows to be implied by this - that he drank 'something', or that the past is real. | |
| From: Fred Dretske (The Case against Closure (and reply) [2005], p.28) | |
| A reaction: A nice case of analogy! He's right about regret. Perceptual and inferential knowledge have different grounds. To deny inferential knowledge seems to be a denial that modus ponens can be a justification. But MP gives truth, not knowledge. |
| 19547 | Reasons for believing P may not transmit to its implication, Q [Dretske] |
| Full Idea: Some reasons for believing P do not transmit to things, Q, known to be implied by P. | |
| From: Fred Dretske (The Case against Closure (and reply) [2005], p.29) | |
| A reaction: That seems true enough. I see someone limping, but infer that their leg is damaged. The only question is whether I should accept the inference. How can I accept that inference, but then back out of that knowledge? |
| 19546 | Knowing by visual perception is not the same as knowing by implication [Dretske] |
| Full Idea: A way of knowing there are cookies in the jar - visual perception - is not a way of knowing what one knows to be implied by this - that visual appearances are not misleading. | |
| From: Fred Dretske (The Case against Closure (and reply) [2005], p.29) | |
| A reaction: Why is the 'way of knowing' relevant? Isn't the only question that of whether implication of a truth is in infallible route to a truth (modus ponens)? If you know THAT it is true, then you must believe it, and implication is top quality justification. No? |
| 19548 | The only way to preserve our homely truths is to abandon closure [Dretske] |
| Full Idea: The only way to preserve knowledge of homely truths, the truths everyone takes themselves to know, is to abandon closure. | |
| From: Fred Dretske (The Case against Closure (and reply) [2005], p.32) | |
| A reaction: His point is that knowledge of homely truths seems to imply knowledge of the background facts needed to support them, which he takes to be an unreasonable requirement. I recommend pursuing contextualism, rather than abandoning closure. |
| 19549 | P may imply Q, but evidence for P doesn't imply evidence for Q, so closure fails [Dretske] |
| Full Idea: The evidence that gives me knowledge of P (there are cookies in the jar) can exist without evidence for knowing Q (they are not fake), despite my knowing that P implies Q. So closure fails. | |
| From: Fred Dretske (The Case against Closure (and reply) [2005], p.33) | |
| A reaction: His more famous example is the zebra. How can P imply Q if there is no evidence for Q? Maybe 'there are cookies in the jar' does not entail they are not fake, once you disambiguate what is being said? |
| 19550 | We know past events by memory, but we don't know the past is real (an implication) by memory [Dretske] |
| Full Idea: The reality of the past (a 'heavyweight implication') ...is something we know to be implied by things we remember, but it is not itself something we remember. | |
| From: Fred Dretske (The Case against Closure (and reply) [2005], p.35) | |
| A reaction: If I begin to doubt that the past is real, then I must necessarily begin to doubt my ordinary memories. This seems to be the modus tollens of knowledge closure. Doesn't that imply that the modus ponens was valid, and closure is correct? |
| 19421 | Souls act as if there were no bodies, and bodies act as if there were no souls [Leibniz] |
| Full Idea: Everything takes place in souls as if there were no body, and everything takes place in bodies as if there were no souls. | |
| From: Gottfried Leibniz (Principle of Life and Plastic Natures [1705], p.198) | |
| A reaction: I don't think I have ever encountered a modern thinker who accepts this view. Leibniz rejected Occasionalism, but his account depends entirely on the role of God, to set up the pre-established harmony. Why would God do that? |
| 19420 | Death and generation are just transformations of an animal, augmented or diminished [Leibniz] |
| Full Idea: Death, like generation, is only the transformation of the same animal, which is sometimes augmented and sometimes diminished. | |
| From: Gottfried Leibniz (Principle of Life and Plastic Natures [1705], p.195) | |
| A reaction: Leibniz has a very unusual view of death, since neither minds nor their bodies can ever be wholly destroyed. Death is a kind of shrinking. I suspect that he was wrong about that. |
| 19416 | Not all of matter is animated, any more than a pond full of living fish is animated [Leibniz] |
| Full Idea: It must not be said that each portion of matter is animated, just as we do not say that a pond full of fishes is an animated body, although a fish is. | |
| From: Gottfried Leibniz (Principle of Life and Plastic Natures [1705], p.190) | |
| A reaction: This is a particularly clear picture of the role of monads in matter. Monads are attached to bodies, which are entirely inanimate, but monads suffuse matter and give it its properties, like particularly bubbly champagne. Cf Idea 19422. |
| 19422 | Every particle of matter contains organic bodies [Leibniz] |
| Full Idea: There is no particle of matter which does not contain organic bodies. | |
| From: Gottfried Leibniz (Principle of Life and Plastic Natures [1705], p.198) | |
| A reaction: Cf Idea 19416. There seems to be an interaction problem here (solved, presumably, by pre-established harmony). The organic bodies are there to explain the active behaviour of matter, but the related matter seems intrinsically inert. |
| 19418 | Mechanics shows that all motion originates in other motion, so there is a Prime Mover [Leibniz] |
| Full Idea: The maxim that there is no motion which has not its origin in another motion, according to the laws of mechanics, leads us again to the Prime Mover. | |
| From: Gottfried Leibniz (Principle of Life and Plastic Natures [1705], p.194) | |
| A reaction: This is Leibniz's endorsement (uncredited) to Aquinas's First Way. It is hard to see how the laws of mechanics could have anything to say about the origin of movement. And doesn't the law say that the motions of God need a mover? |
| 19417 | All substances are in harmony, even though separate, so they must have one divine cause [Leibniz] |
| Full Idea: My system of Pre-established Harmony furnishes a new proof of God's existence, since it is manifest that the agreement of so many substances, of which the one has no influence upon the other, could only come from a general cause on which they all depend. | |
| From: Gottfried Leibniz (Principle of Life and Plastic Natures [1705], p.192) | |
| A reaction: Adjacent harmony seems self-explanatory, but remote harmony is interesting evidence for God. Hence modern quantum non-locality should make us all wonder whether there is a deeper explanation. |