80 ideas
8721 | An 'impredicative' definition seems circular, because it uses the term being defined [Friend] |
8680 | Classical definitions attempt to refer, but intuitionist/constructivist definitions actually create objects [Friend] |
18889 | Ostensive definitions needn't involve pointing, but must refer to something specific [Salmon,N] |
3678 | Reductio ad absurdum proves an idea by showing that its denial produces contradiction [Friend] |
8705 | Anti-realists see truth as our servant, and epistemically contrained [Friend] |
8713 | In classical/realist logic the connectives are defined by truth-tables [Friend] |
14684 | A world is 'accessible' to another iff the first is possible according to the second [Salmon,N] |
14669 | For metaphysics, T may be the only correct system of modal logic [Salmon,N] |
14667 | System B has not been justified as fallacy-free for reasoning on what might have been [Salmon,N] |
14668 | In B it seems logically possible to have both p true and p is necessarily possibly false [Salmon,N] |
14692 | System B implies that possibly-being-realized is an essential property of the world [Salmon,N] |
14671 | What is necessary is not always necessarily necessary, so S4 is fallacious [Salmon,N] |
14627 | S4, and therefore S5, are invalid for metaphysical modality [Salmon,N, by Williamson] |
14686 | S5 modal logic ignores accessibility altogether [Salmon,N] |
14691 | S5 believers say that-things-might-have-been-that-way is essential to ways things might have been [Salmon,N] |
14693 | The unsatisfactory counterpart-theory allows the retention of S5 [Salmon,N] |
14670 | Metaphysical (alethic) modal logic concerns simple necessity and possibility (not physical, epistemic..) [Salmon,N] |
8708 | Double negation elimination is not valid in intuitionist logic [Friend] |
8694 | Free logic was developed for fictional or non-existent objects [Friend] |
8665 | A 'proper subset' of A contains only members of A, but not all of them [Friend] |
8672 | A 'powerset' is all the subsets of a set [Friend] |
8677 | Set theory makes a minimum ontological claim, that the empty set exists [Friend] |
8666 | Infinite sets correspond one-to-one with a subset [Friend] |
8682 | Major set theories differ in their axioms, and also over the additional axioms of choice and infinity [Friend] |
8709 | The law of excluded middle is syntactic; it just says A or not-A, not whether they are true or false [Friend] |
8711 | Intuitionists read the universal quantifier as "we have a procedure for checking every..." [Friend] |
8675 | Paradoxes can be solved by talking more loosely of 'classes' instead of 'sets' [Friend] |
8674 | The Burali-Forti paradox asks whether the set of all ordinals is itself an ordinal [Friend] |
8667 | The 'integers' are the positive and negative natural numbers, plus zero [Friend] |
8668 | The 'rational' numbers are those representable as fractions [Friend] |
8670 | A number is 'irrational' if it cannot be represented as a fraction [Friend] |
8661 | The natural numbers are primitive, and the ordinals are up one level of abstraction [Friend] |
8664 | Cardinal numbers answer 'how many?', with the order being irrelevant [Friend] |
8671 | The 'real' numbers (rationals and irrationals combined) is the Continuum, which has no gaps [Friend] |
8663 | Raising omega to successive powers of omega reveal an infinity of infinities [Friend] |
8662 | The first limit ordinal is omega (greater, but without predecessor), and the second is twice-omega [Friend] |
8669 | Between any two rational numbers there is an infinite number of rational numbers [Friend] |
8676 | Is mathematics based on sets, types, categories, models or topology? [Friend] |
8678 | Most mathematical theories can be translated into the language of set theory [Friend] |
8701 | The number 8 in isolation from the other numbers is of no interest [Friend] |
8702 | In structuralism the number 8 is not quite the same in different structures, only equivalent [Friend] |
8699 | Are structures 'ante rem' (before reality), or are they 'in re' (grounded in physics)? [Friend] |
8696 | Structuralist says maths concerns concepts about base objects, not base objects themselves [Friend] |
8695 | Structuralism focuses on relations, predicates and functions, with objects being inessential [Friend] |
8700 | 'In re' structuralism says that the process of abstraction is pattern-spotting [Friend] |
8681 | The big problem for platonists is epistemic: how do we perceive, intuit, know or detect mathematical facts? [Friend] |
8712 | Mathematics should be treated as true whenever it is indispensable to our best physical theory [Friend] |
8716 | Formalism is unconstrained, so cannot indicate importance, or directions for research [Friend] |
8706 | Constructivism rejects too much mathematics [Friend] |
8707 | Intuitionists typically retain bivalence but reject the law of excluded middle [Friend] |
16062 | A necessary relation between fact-levels seems to be a further irreducible fact [Lynch/Glasgow] |
16061 | If some facts 'logically supervene' on some others, they just redescribe them, adding nothing [Lynch/Glasgow] |
16060 | Nonreductive materialism says upper 'levels' depend on lower, but don't 'reduce' [Lynch/Glasgow] |
16064 | The hallmark of physicalism is that each causal power has a base causal power under it [Lynch/Glasgow] |
14742 | It can't be indeterminate whether x and y are identical; if x,y is indeterminate, then it isn't x,x [Salmon,N] |
8704 | Structuralists call a mathematical 'object' simply a 'place in a structure' [Friend] |
18888 | Essentialism says some properties must be possessed, if a thing is to exist [Salmon,N] |
14678 | Any property is attached to anything in some possible world, so I am a radical anti-essentialist [Salmon,N] |
14680 | Logical possibility contains metaphysical possibility, which contains nomological possibility [Salmon,N] |
14690 | In the S5 account, nested modalities may be unseen, but they are still there [Salmon,N] |
14677 | Metaphysical necessity is said to be unrestricted necessity, true in every world whatsoever [Salmon,N] |
14679 | Bizarre identities are logically but not metaphysically possible, so metaphysical modality is restricted [Salmon,N] |
14688 | Without impossible worlds, the unrestricted modality that is metaphysical has S5 logic [Salmon,N] |
14685 | Metaphysical necessity is NOT truth in all (unrestricted) worlds; necessity comes first, and is restricted [Salmon,N] |
14681 | Logical necessity is free of constraints, and may accommodate all of S5 logic [Salmon,N] |
14676 | Nomological necessity is expressed with intransitive relations in modal semantics [Salmon,N] |
14689 | Necessity and possibility are not just necessity and possibility according to the actual world [Salmon,N] |
14674 | Impossible worlds are also ways for things to be [Salmon,N] |
14682 | Denial of impossible worlds involves two different confusions [Salmon,N] |
14687 | Without impossible worlds, how things might have been is the only way for things to be [Salmon,N] |
14683 | Possible worlds rely on what might have been, so they can' be used to define or analyse modality [Salmon,N] |
14672 | Possible worlds are maximal abstract ways that things might have been [Salmon,N] |
14675 | Possible worlds just have to be 'maximal', but they don't have to be consistent [Salmon,N] |
14673 | You can't define worlds as sets of propositions, and then define propositions using worlds [Salmon,N] |
8685 | Studying biology presumes the laws of chemistry, and it could never contradict them [Friend] |
8688 | Concepts can be presented extensionally (as objects) or intensionally (as a characterization) [Friend] |
18886 | Frege's 'sense' solves four tricky puzzles [Salmon,N] |
18887 | The perfect case of direct reference is a variable which has been assigned a value [Salmon,N] |
18885 | Kripke and Putnam made false claims that direct reference implies essentialism [Salmon,N] |
18891 | Nothing in the direct theory of reference blocks anti-essentialism; water structure might have been different [Salmon,N] |