65 ideas
13466 | We are all post-Kantians, because he set the current agenda for philosophy [Hart,WD] |
Full Idea: We are all post-Kantians, ...because Kant set an agenda for philosophy that we are still working through. | |
From: William D. Hart (The Evolution of Logic [2010], 2) | |
A reaction: Hart says that the main agenda is set by Kant's desire to defend the principle of sufficient reason against Hume's attack on causation. I would take it more generally to be the assessment of metaphysics, and of a priori knowledge. |
13477 | The problems are the monuments of philosophy [Hart,WD] |
Full Idea: The real monuments of philosophy are its problems. | |
From: William D. Hart (The Evolution of Logic [2010], 2) | |
A reaction: Presumably he means '....rather than its solutions'. No other subject would be very happy with that sort of claim. Compare Idea 8243. A complaint against analytic philosophy is that it has achieved no consensus at all. |
13515 | To study abstract problems, some knowledge of set theory is essential [Hart,WD] |
Full Idea: By now, no education in abstract pursuits is adequate without some familiarity with sets. | |
From: William D. Hart (The Evolution of Logic [2010], 10) | |
A reaction: A heart-sinking observation for those who aspire to study metaphysics and modality. The question is, what will count as 'some' familiarity? Are only professional logicians now allowed to be proper philosophers? |
13469 | Tarski showed how we could have a correspondence theory of truth, without using 'facts' [Hart,WD] |
Full Idea: It is an ancient and honourable view that truth is correspondence to fact; Tarski showed us how to do without facts here. | |
From: William D. Hart (The Evolution of Logic [2010], 2) | |
A reaction: This is a very interesting spin on Tarski, who certainly seems to endorse the correspondence theory, even while apparently inventing a new 'semantic' theory of truth. It is controversial how far Tarski's theory really is a 'correspondence' theory. |
13504 | Truth for sentences is satisfaction of formulae; for sentences, either all sequences satisfy it (true) or none do [Hart,WD] |
Full Idea: We explain truth for sentences in terms of satisfaction of formulae. The crux here is that for a sentence, either all sequences satisfy it or none do (with no middle ground). For formulae, some sequences may satisfy it and others not. | |
From: William D. Hart (The Evolution of Logic [2010], 4) | |
A reaction: This is the hardest part of Tarski's theory of truth to grasp. |
13503 | A first-order language has an infinity of T-sentences, which cannot add up to a definition of truth [Hart,WD] |
Full Idea: In any first-order language, there are infinitely many T-sentences. Since definitions should be finite, the agglomeration of all the T-sentences is not a definition of truth. | |
From: William D. Hart (The Evolution of Logic [2010], 4) | |
A reaction: This may be a warning shot aimed at Davidson's extensive use of Tarski's formal account in his own views on meaning in natural language. |
13500 | Conditional Proof: infer a conditional, if the consequent can be deduced from the antecedent [Hart,WD] |
Full Idea: A 'conditional proof' licenses inferences to a conditional from a deduction of its consequent from its antecedent. | |
From: William D. Hart (The Evolution of Logic [2010], 4) | |
A reaction: That is, a proof can be enshrined in an arrow. |
13502 | ∃y... is read as 'There exists an individual, call it y, such that...', and not 'There exists a y such that...' [Hart,WD] |
Full Idea: When a quantifier is attached to a variable, as in '∃(y)....', then it should be read as 'There exists an individual, call it y, such that....'. One should not read it as 'There exists a y such that...', which would attach predicate to quantifier. | |
From: William D. Hart (The Evolution of Logic [2010], 4) | |
A reaction: The point is to make clear that in classical logic the predicates attach to the objects, and not to some formal component like a quantifier. |
7791 | The simplest of the logics based on possible worlds is Lewis's S5 [Lewis,CI, by Girle] |
Full Idea: C.I.Lewis constructed five axiomatic systems of modal logic, and named them S1 to S5. It turns out that the simplest of the logics based on possible worlds is the same as Lewis's S5. | |
From: report of C.I. Lewis (works [1935]) by Rod Girle - Modal Logics and Philosophy 2.1 | |
A reaction: Nathan Salmon ('Reference and Essence' 2nd ed) claims (on p.xvii) that "the correct modal logic is weaker than S5 and weaker even than S4". Which is the greater virtue, simplicity or weakness? |
13456 | Set theory articulates the concept of order (through relations) [Hart,WD] |
Full Idea: It is set theory, and more specifically the theory of relations, that articulates order. | |
From: William D. Hart (The Evolution of Logic [2010]) | |
A reaction: It would seem that we mainly need set theory in order to talk accurately about order, and about infinity. The two come together in the study of the ordinal numbers. |
13497 | Nowadays ZFC and NBG are the set theories; types are dead, and NF is only useful for the whole universe [Hart,WD] |
Full Idea: The theory of types is a thing of the past. There is now nothing to choose between ZFC and NBG (Neumann-Bernays-Gödel). NF (Quine's) is a more specialized taste, but is a place to look if you want the universe. | |
From: William D. Hart (The Evolution of Logic [2010], 3) |
13443 | ∈ relates across layers, while ⊆ relates within layers [Hart,WD] |
Full Idea: ∈ relates across layers (Plato is a member of his unit set and the set of people), while ⊆ relates within layers (the singleton of Plato is a subset of the set of people). This distinction only became clear in the 19th century. | |
From: William D. Hart (The Evolution of Logic [2010], 1) | |
A reaction: Getting these two clear may be the most important distinction needed to understand how set theory works. |
13442 | Without the empty set we could not form a∩b without checking that a and b meet [Hart,WD] |
Full Idea: Without the empty set, disjoint sets would have no intersection, and we could not form a∩b without checking that a and b meet. This is an example of the utility of the empty set. | |
From: William D. Hart (The Evolution of Logic [2010], 1) | |
A reaction: A novice might plausibly ask why there should be an intersection for every pair of sets, if they have nothing in common except for containing this little puff of nothingness. But then what do novices know? |
13493 | In the modern view, foundation is the heart of the way to do set theory [Hart,WD] |
Full Idea: In the second half of the twentieth century there emerged the opinion that foundation is the heart of the way to do set theory. | |
From: William D. Hart (The Evolution of Logic [2010], 3) | |
A reaction: It is foundation which is the central axiom of the iterative conception of sets, where each level of sets is built on previous levels, and they are all 'well-founded'. |
13495 | Foundation Axiom: an nonempty set has a member disjoint from it [Hart,WD] |
Full Idea: The usual statement of Foundation is that any nonempty set has a member disjoint from it. This phrasing is ordinal-free and closer to the primitives of ZFC. | |
From: William D. Hart (The Evolution of Logic [2010], 3) |
13461 | We can choose from finite and evident sets, but not from infinite opaque ones [Hart,WD] |
Full Idea: When a set is finite, we can prove it has a choice function (∀x x∈A → f(x)∈A), but we need an axiom when A is infinite and the members opaque. From infinite shoes we can pick a left one, but from socks we need the axiom of choice. | |
From: William D. Hart (The Evolution of Logic [2010], 1) | |
A reaction: The socks example in from Russell 1919:126. |
13462 | With the Axiom of Choice every set can be well-ordered [Hart,WD] |
Full Idea: It follows from the Axiom of Choice that every set can be well-ordered. | |
From: William D. Hart (The Evolution of Logic [2010], 1) | |
A reaction: For 'well-ordered' see Idea 13460. Every set can be ordered with a least member. |
13516 | If we accept that V=L, it seems to settle all the open questions of set theory [Hart,WD] |
Full Idea: It has been said (by Burt Dreben) that the only reason set theorists do not generally buy the view that V = L is that it would put them out of business by settling their open questions. | |
From: William D. Hart (The Evolution of Logic [2010], 10) | |
A reaction: Hart says V=L breaks with the interative conception of sets at level ω+1, which is countable is the constructible view, but has continuum many in the cumulative (iterative) hierarch. The constructible V=L view is anti-platonist. |
13441 | Naïve set theory has trouble with comprehension, the claim that every predicate has an extension [Hart,WD] |
Full Idea: 'Comprehension' is the assumption that every predicate has an extension. Naïve set theory is the theory whose axioms are extensionality and comprehension, and comprehension is thought to be its naivety. | |
From: William D. Hart (The Evolution of Logic [2010], 1) | |
A reaction: This doesn't, of course, mean that there couldn't be a more modest version of comprehension. The notorious difficulty come with the discovery of self-referring predicates which can't possibly have extensions. |
13494 | The iterative conception may not be necessary, and may have fixed points or infinitely descending chains [Hart,WD] |
Full Idea: That the iterative sets suffice for most of ZFC does not show they are necessary, nor is it evident that the set of operations has no fixed points (as 0 is a fixed point for square-of), and no infinitely descending chains (like negative integers). | |
From: William D. Hart (The Evolution of Logic [2010], 3) | |
A reaction: People don't seem to worry that they aren't 'necessary', and further measures are possible to block infinitely descending chains. |
13457 | A 'partial ordering' is irreflexive and transitive; the sets are ordered, but not the subsets [Hart,WD] |
Full Idea: We say that a binary relation R 'partially orders' a field A just in case R is irreflexive (so that nothing bears R to itself) and transitive. When the set is {a,b}, its subsets {a} and {b} are incomparable in a partial ordering. | |
From: William D. Hart (The Evolution of Logic [2010], 1) |
13458 | A partial ordering becomes 'total' if any two members of its field are comparable [Hart,WD] |
Full Idea: A partial ordering is a 'total ordering' just in case any two members of its field are comparable, that is, either a is R to b, or b is R to a, or a is b. | |
From: William D. Hart (The Evolution of Logic [2010], 1) | |
A reaction: See Idea 13457 for 'partial ordering'. The three conditions are known as the 'trichotomy' condition. |
13490 | Von Neumann defines α<β as α∈β [Hart,WD] |
Full Idea: One of the glories of Von Neumann's theory of numbers is to define α < β to mean that α ∈ β. | |
From: William D. Hart (The Evolution of Logic [2010], 3) |
13460 | 'Well-ordering' must have a least member, so it does the natural numbers but not the integers [Hart,WD] |
Full Idea: A total order 'well-orders' its field just in case any nonempty subset B of its field has an R-least member, that is, there is a b in B such that for any a in B different from b, b bears R to a. So less-than well-orders natural numbers, but not integers. | |
From: William D. Hart (The Evolution of Logic [2010], 1) | |
A reaction: The natural numbers have a starting point, but the integers are infinite in both directions. In plain English, an order is 'well-ordered' if there is a starting point. |
13481 | Maybe sets should be rethought in terms of the even more basic categories [Hart,WD] |
Full Idea: Some have claimed that sets should be rethought in terms of still more basic things, categories. | |
From: William D. Hart (The Evolution of Logic [2010], 2) | |
A reaction: [He cites F.William Lawvere 1966] It appears to the the context of foundations for mathematics that he has in mind. |
9358 | There are several logics, none of which will ever derive falsehoods from truth [Lewis,CI] |
Full Idea: The fact is that there are several logics, markedly different, each self-consistent in its own terms and such that whoever, using it, avoids false premises, will never reach a false conclusion. | |
From: C.I. Lewis (A Pragmatic Conception of the A Priori [1923], p.366) | |
A reaction: As the man who invented modal logic in five different versions, he speaks with some authority. Logicians now debate which version is the best, so how could that be decided? You could avoid false conclusions by never reasoning at all. |
9357 | Excluded middle is just our preference for a simplified dichotomy in experience [Lewis,CI] |
Full Idea: The law of excluded middle formulates our decision that whatever is not designated by a certain term shall be designated by its negative. It declares our purpose to make a complete dichotomy of experience, ..which is only our penchant for simplicity. | |
From: C.I. Lewis (A Pragmatic Conception of the A Priori [1923], p.365) | |
A reaction: I find this view quite appealing. 'Look, it's either F or it isn't!' is a dogmatic attitude which irritates a lot of people, and appears to be dispensible. Intuitionists in mathematics dispense with the principle, and vagueness threatens it. |
9364 | Names represent a uniformity in experience, or they name nothing [Lewis,CI] |
Full Idea: A name must represent some uniformity in experience or it names nothing. | |
From: C.I. Lewis (A Pragmatic Conception of the A Priori [1923], p.368) | |
A reaction: I like this because, in the quintessentially linguistic debate about the exact logical role of names, it reminds us that names arise because of the way reality is; they are not sui generis private games for logicians. |
13506 | The universal quantifier can't really mean 'all', because there is no universal set [Hart,WD] |
Full Idea: All the main set theories deny that there is a set of which everything is a member. No interpretation has a domain with everything in it. So the universal quantifier never gets to mean everything all at once; 'all' does not mean all. | |
From: William D. Hart (The Evolution of Logic [2010], 4) | |
A reaction: Could you have an 'uncompleted' universal set, in the spirit of uncompleted infinities? In ordinary English we can talk about 'absolutely everything' - we just can't define a set of everything. Must we 'define' our domain? |
13513 | Models are ways the world might be from a first-order point of view [Hart,WD] |
Full Idea: Models are ways the world might be from a first-order point of view. | |
From: William D. Hart (The Evolution of Logic [2010], 9) |
13505 | Model theory studies how set theory can model sets of sentences [Hart,WD] |
Full Idea: Modern model theory investigates which set theoretic structures are models for which collections of sentences. | |
From: William D. Hart (The Evolution of Logic [2010], 4) | |
A reaction: So first you must choose your set theory (see Idea 13497). Then you presumably look at how to formalise sentences, and then look at the really tricky ones, many of which will involve various degrees of infinity. |
13511 | Model theory is mostly confined to first-order theories [Hart,WD] |
Full Idea: There is no developed methematics of models for second-order theories, so for the most part, model theory is about models for first-order theories. | |
From: William D. Hart (The Evolution of Logic [2010], 9) |
13512 | Modern model theory begins with the proof of Los's Conjecture in 1962 [Hart,WD] |
Full Idea: The beginning of modern model theory was when Morley proved Los's Conjecture in 1962 - that a complete theory in a countable language categorical in one uncountable cardinal is categorical in all. | |
From: William D. Hart (The Evolution of Logic [2010], 9) |
13496 | First-order logic is 'compact': consequences of a set are consequences of a finite subset [Hart,WD] |
Full Idea: First-order logic is 'compact', which means that any logical consequence of a set (finite or infinite) of first-order sentences is a logical consequence of a finite subset of those sentences. | |
From: William D. Hart (The Evolution of Logic [2010], 3) |
13484 | Berry's Paradox: we succeed in referring to a number, with a term which says we can't do that [Hart,WD] |
Full Idea: Berry's Paradox: by the least number principle 'the least number denoted by no description of fewer than 79 letters' exists, but we just referred to it using a description of 77 letters. | |
From: William D. Hart (The Evolution of Logic [2010], 3) | |
A reaction: I struggle with this. If I refer to 'an object to which no human being could possibly refer', have I just referred to something? Graham Priest likes this sort of idea. |
13482 | The Burali-Forti paradox is a crisis for Cantor's ordinals [Hart,WD] |
Full Idea: The Burali-Forti Paradox was a crisis for Cantor's theory of ordinal numbers. | |
From: William D. Hart (The Evolution of Logic [2010], 3) |
13507 | The machinery used to solve the Liar can be rejigged to produce a new Liar [Hart,WD] |
Full Idea: In effect, the machinery introduced to solve the liar can always be rejigged to yield another version the liar. | |
From: William D. Hart (The Evolution of Logic [2010], 4) | |
A reaction: [He cites Hans Herzberger 1980-81] The machinery is Tarski's device of only talking about sentences of a language by using a 'metalanguage'. |
9117 | The smallest heap has four objects: three on the bottom, one on the top [Hart,WD, by Sorensen] |
Full Idea: Hart argues that the smallest heap consists of four objects: three on the bottom, one on the top. | |
From: report of William D. Hart (Hat-Tricks and Heaps [1992]) by Roy Sorensen - Vagueness and Contradiction Intro | |
A reaction: If the objects were rough bolders, you could get away with two on the bottom. He's wrong. No one would accept as a 'heap' four minute grains barely visible to the naked eye. No one would describe such a group of items in a supermarket as a heap. |
13459 | The less-than relation < well-orders, and partially orders, and totally orders the ordinal numbers [Hart,WD] |
Full Idea: We can show (using the axiom of choice) that the less-than relation, <, well-orders the ordinals, ...and that it partially orders the ordinals, ...and that it totally orders the ordinals. | |
From: William D. Hart (The Evolution of Logic [2010], 1) |
13463 | There are at least as many infinite cardinals as transfinite ordinals (because they will map) [Hart,WD] |
Full Idea: Since we can map the transfinite ordinals one-one into the infinite cardinals, there are at least as many infinite cardinals as transfinite ordinals. | |
From: William D. Hart (The Evolution of Logic [2010], 1) |
13491 | The axiom of infinity with separation gives a least limit ordinal ω [Hart,WD] |
Full Idea: The axiom of infinity with separation yields a least limit ordinal, which is called ω. | |
From: William D. Hart (The Evolution of Logic [2010], 3) |
13492 | Von Neumann's ordinals generalise into the transfinite better, because Zermelo's ω is a singleton [Hart,WD] |
Full Idea: It is easier to generalize von Neumann's finite ordinals into the transfinite. All Zermelo's nonzero finite ordinals are singletons, but if ω were a singleton it is hard to see how if could fail to be the successor of its member and so not a limit. | |
From: William D. Hart (The Evolution of Logic [2010], 3) |
13446 | 19th century arithmetization of analysis isolated the real numbers from geometry [Hart,WD] |
Full Idea: The real numbers were not isolated from geometry until the arithmetization of analysis during the nineteenth century. | |
From: William D. Hart (The Evolution of Logic [2010], 1) |
13509 | We can establish truths about infinite numbers by means of induction [Hart,WD] |
Full Idea: Mathematical induction is a way to establish truths about the infinity of natural numbers by a finite proof. | |
From: William D. Hart (The Evolution of Logic [2010], 5) | |
A reaction: If there are truths about infinities, it is very tempting to infer that the infinities must therefore 'exist'. A nice, and large, question in philosophy is whether there can be truths without corresponding implications of existence. |
13474 | Euclid has a unique parallel, spherical geometry has none, and saddle geometry has several [Hart,WD] |
Full Idea: There is a familiar comparison between Euclid (unique parallel) and 'spherical' geometry (no parallel) and 'saddle' geometry (several parallels). | |
From: William D. Hart (The Evolution of Logic [2010], 2) |
13471 | Mathematics makes existence claims, but philosophers usually say those are never analytic [Hart,WD] |
Full Idea: The thesis that no existence proposition is analytic is one of the few constants in philosophical consciences, but there are many existence claims in mathematics, such as the infinity of primes, five regular solids, and certain undecidable propositions. | |
From: William D. Hart (The Evolution of Logic [2010], 2) |
16062 | A necessary relation between fact-levels seems to be a further irreducible fact [Lynch/Glasgow] |
Full Idea: It seems unavoidable that the facts about logically necessary relations between levels of facts are themselves logically distinct further facts, irreducible to the microphysical facts. | |
From: Lynch,MP/Glasgow,JM (The Impossibility of Superdupervenience [2003], C) | |
A reaction: I'm beginning to think that rejecting every theory of reality that is proposed by carefully exposing some infinite regress hidden in it is a rather lazy way to do philosophy. Almost as bad as rejecting anything if it can't be defined. |
16061 | If some facts 'logically supervene' on some others, they just redescribe them, adding nothing [Lynch/Glasgow] |
Full Idea: Logical supervenience, restricted to individuals, seems to imply strong reduction. It is said that where the B-facts logically supervene on the A-facts, the B-facts simply re-describe what the A-facts describe, and the B-facts come along 'for free'. | |
From: Lynch,MP/Glasgow,JM (The Impossibility of Superdupervenience [2003], C) | |
A reaction: This seems to be taking 'logically' to mean 'analytically'. Presumably an entailment is logically supervenient on its premisses, and may therefore be very revealing, even if some people think such things are analytic. |
13488 | Mass words do not have plurals, or numerical adjectives, or use 'fewer' [Hart,WD] |
Full Idea: Jespersen calls a noun a mass word when it has no plural, does not take numerical adjectives, and does not take 'fewer'. | |
From: William D. Hart (The Evolution of Logic [2010], 3) | |
A reaction: Jespersen was a great linguistics expert. |
16060 | Nonreductive materialism says upper 'levels' depend on lower, but don't 'reduce' [Lynch/Glasgow] |
Full Idea: The root intuition behind nonreductive materialism is that reality is composed of ontologically distinct layers or levels. …The upper levels depend on the physical without reducing to it. | |
From: Lynch,MP/Glasgow,JM (The Impossibility of Superdupervenience [2003], B) | |
A reaction: A nice clear statement of a view which I take to be false. This relationship is the sort of thing that drives people fishing for an account of it to use the word 'supervenience', which just says two things seem to hang out together. Fluffy materialism. |
16064 | The hallmark of physicalism is that each causal power has a base causal power under it [Lynch/Glasgow] |
Full Idea: Jessica Wilson (1999) says what makes physicalist accounts different from emergentism etc. is that each individual causal power associated with a supervenient property is numerically identical with a causal power associated with its base property. | |
From: Lynch,MP/Glasgow,JM (The Impossibility of Superdupervenience [2003], n 11) | |
A reaction: Hence the key thought in so-called (serious, rather than self-evident) 'emergentism' is so-called 'downward causation', which I take to be an idle daydream. |
11002 | Equating necessity with informal provability is the S4 conception of necessity [Lewis,CI, by Read] |
Full Idea: C.I.Lewis's S4 system develops a sense of necessity as 'provability' in some fairly informal sense. | |
From: report of C.I. Lewis (works [1935]) by Stephen Read - Thinking About Logic Ch. 4 |
9362 | Necessary truths are those we will maintain no matter what [Lewis,CI] |
Full Idea: Those laws and those laws only have necessary truth which we are prepared to maintain, no matter what. | |
From: C.I. Lewis (A Pragmatic Conception of the A Priori [1923], p.367) | |
A reaction: This bold and simple claim has famously been torpedoed by a well-known counterexample - that virtually every human being will cling on to the proposition "dogs have at some time existed" no matter what, but it clearly isn't a necessary truth. |
7803 | Modal logic began with translation difficulties for 'If...then' [Lewis,CI, by Girle] |
Full Idea: C.I.Lewis began his groundbreaking work in modal logic because he was concerned about the unreliability of the material conditional as a translation of 'If ... then' conditionals. | |
From: report of C.I. Lewis (Symbolic Logic (with Langford) [1932]) by Rod Girle - Modal Logics and Philosophy 12.3 | |
A reaction: Compare 'if this is square then it has four corners' with 'if it rains then our afternoon is ruined'. Different modalities seem to be involved. We even find that 'a square has four corners' will be materially implied if it rains! |
13480 | Fregean self-evidence is an intrinsic property of basic truths, rules and definitions [Hart,WD] |
Full Idea: The conception of Frege is that self-evidence is an intrinsic property of the basic truths, rules, and thoughts expressed by definitions. | |
From: William D. Hart (The Evolution of Logic [2010], p.350) | |
A reaction: The problem is always that what appears to be self-evident may turn out to be wrong. Presumably the effort of arriving at a definition ought to clarify and support the self-evident ingredient. |
9365 | We can maintain a priori principles come what may, but we can also change them [Lewis,CI] |
Full Idea: The a priori contains principles which can be maintained in the face of all experience, representing the initiative of the mind. But they are subject to alteration on pragmatic grounds, if expanding experience shows their intellectual infelicity. | |
From: C.I. Lewis (A Pragmatic Conception of the A Priori [1923], p.373) | |
A reaction: [compressed] This simply IS Quine's famous 'web of belief' picture, showing how firmly Quine is in the pragmatist tradition. Lewis treats a priori principles as a pragmatic toolkit, which can be refined to be more effective. Not implausible... |
13476 | The failure of key assumptions in geometry, mereology and set theory throw doubt on the a priori [Hart,WD] |
Full Idea: In the case of the parallels postulate, Euclid's fifth axiom (the whole is greater than the part), and comprehension, saying was believing for a while, but what was said was false. This should make a shrewd philosopher sceptical about a priori knowledge. | |
From: William D. Hart (The Evolution of Logic [2010], 2) | |
A reaction: Euclid's fifth is challenged by infinite numbers, and comprehension is challenged by Russell's paradox. I can't see a defender of the a priori being greatly worried about these cases. No one ever said we would be right - in doing arithmetic, for example. |
21500 | We rely on memory for empirical beliefs because they mutually support one another [Lewis,CI] |
Full Idea: When the whole range of empirical beliefs is taken into account, all of them more or less dependent on memorial knowledge, we find that those which are most credible can be assured by their mutual support, or 'congruence'. | |
From: C.I. Lewis (An Analysis of Knowledge and Valuation [1946], 334), quoted by Erik J. Olsson - Against Coherence 3.1 | |
A reaction: Lewis may be over-confident about this, and is duly attacked by Olson, but it seems to me roughly correct. How do you assess whether some unusual element in your memory was a dream or a real experience? |
21501 | If we doubt memories we cannot assess our doubt, or what is being doubted [Lewis,CI] |
Full Idea: To doubt our sense of past experience as founded in actuality, would be to lose any criterion by which either the doubt itself or what is doubted could be corroborated. | |
From: C.I. Lewis (An Analysis of Knowledge and Valuation [1946], 358), quoted by Erik J. Olsson - Against Coherence 3.3.1 | |
A reaction: Obviously scepticism about memory can come in degrees, but total rejection of short-term and clear memories looks like a non-starter. What could you put in its place? Hyper-rationalism? Even maths needs memory. |
6556 | If anything is to be probable, then something must be certain [Lewis,CI] |
Full Idea: If anything is to be probable, then something must be certain. | |
From: C.I. Lewis (An Analysis of Knowledge and Valuation [1946], 186), quoted by Robert Fogelin - Walking the Tightrope of Reason Intro | |
A reaction: Lewis makes this comment when facing infinite regress problems. It is a very nice slogan for foundationalism, which embodies the slippery slope view. Personally I feel the emotional pull of foundations, but acknowledge the very strong doubts about them. |
21498 | Congruents assertions increase the probability of each individual assertion in the set [Lewis,CI] |
Full Idea: A set of statements, or a set of supposed facts asserted, will be said to be congruent if and only if they are so related that the antecedent probability of any one of them will be increased if the remainder of the set can be assumed as given premises. | |
From: C.I. Lewis (An Analysis of Knowledge and Valuation [1946], 338), quoted by Erik J. Olsson - Against Coherence 2.2 | |
A reaction: This thesis is vigorously attacked by Erik Olson, who works through the probability calculations. There seems an obvious problem without that. How else do you assess 'congruence', other than by evidence of mutual strengthening? |
5828 | Extension is the class of things, intension is the correct definition of the thing, and intension determines extension [Lewis,CI] |
Full Idea: "The denotation or extension of a term is the class of all actual or existent things which the term correctly applies to or names; the connotation or intension of a term is delimited by any correct definition of it." ..And intension determines extension. | |
From: C.I. Lewis (An Analysis of Knowledge and Valuation [1946]), quoted by Stephen P. Schwartz - Intro to Naming,Necessity and Natural Kinds §II | |
A reaction: The last part is one of the big ideas in philosophy of language, which was rejected by Putnam and co. If you were to reverse the slogan, though, (to extension determines intension) how would you identify the members of the extension? |
13475 | The Fregean concept of GREEN is a function assigning true to green things, and false to the rest [Hart,WD] |
Full Idea: A Fregean concept is a function that assigns to each object a truth value. So instead of the colour green, the concept GREEN assigns truth to each green thing, but falsity to anything else. | |
From: William D. Hart (The Evolution of Logic [2010], 2) | |
A reaction: This would seem to immediately hit the renate/cordate problem, if there was a world in which all and only the green things happened to be square. How could Frege then distinguish the green from the square? Compare Idea 8245. |
9361 | We have to separate the mathematical from physical phenomena by abstraction [Lewis,CI] |
Full Idea: Physical processes present us with phenomena in which the purely mathematical has to be separated out by abstraction. | |
From: C.I. Lewis (A Pragmatic Conception of the A Priori [1923], p.367) | |
A reaction: This is the father of modal logic endorsing traditional abstractionism, it seems. He is also, though, endorsing the view that a priori knowledge is created by us, with pragmatic ends in view. |
9363 | Science seeks classification which will discover laws, essences, and predictions [Lewis,CI] |
Full Idea: The scientific search is for such classification as will make it possible to correlate appearance and behaviour, to discover law, to penetrate to the "essential nature" of things in order that behaviour may become predictable. | |
From: C.I. Lewis (A Pragmatic Conception of the A Priori [1923], p.368) | |
A reaction: Modern scientific essentialists no longer invoke scare quotes, and I think we should talk of the search for the 'mechanisms' which explain behaviour, but Lewis seems to have been sixty years ahead of his time. |