65 ideas
17275 | Realist metaphysics concerns what is real; naive metaphysics concerns natures of things [Fine,K] |
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] |
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] |
17282 | Truths need not always have their source in what exists [Fine,K] |
17283 | If the truth-making relation is modal, then modal truths will be grounded in anything [Fine,K] |
8713 | In classical/realist logic the connectives are defined by truth-tables [Friend] |
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] |
17286 | Logical consequence is verification by a possible world within a truth-set [Fine,K] |
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] |
17272 | 2+2=4 is necessary if it is snowing, but not true in virtue of the fact that it is snowing [Fine,K] |
17276 | If you say one thing causes another, that leaves open that the 'other' has its own distinct reality [Fine,K] |
17284 | An immediate ground is the next lower level, which gives the concept of a hierarchy [Fine,K] |
17285 | 'Strict' ground moves down the explanations, but 'weak' ground can move sideways [Fine,K] |
17288 | We learn grounding from what is grounded, not what does the grounding [Fine,K] |
17280 | Ground is best understood as a sentence operator, rather than a relation between predicates [Fine,K] |
17281 | If grounding is a relation it must be between entities of the same type, preferably between facts [Fine,K] |
17290 | Only metaphysical grounding must be explained by essence [Fine,K] |
17274 | Philosophical explanation is largely by ground (just as cause is used in science) [Fine,K] |
17278 | We can only explain how a reduction is possible if we accept the concept of ground [Fine,K] |
17287 | Facts, such as redness and roundness of a ball, can be 'fused' into one fact [Fine,K] |
8704 | Structuralists call a mathematical 'object' simply a 'place in a structure' [Friend] |
17279 | Even a three-dimensionalist might identify temporal parts, in their thinking [Fine,K] |
17289 | Every necessary truth is grounded in the nature of something [Fine,K] |
17273 | Each basic modality has its 'own' explanatory relation [Fine,K] |
19540 | Don't confuse justified belief with justified believers [Dougherty/Rysiew] |
19539 | If knowledge is unanalysable, that makes justification more important [Dougherty/Rysiew] |
17271 | Is there metaphysical explanation (as well as causal), involving a constitutive form of determination? [Fine,K] |
17291 | We explain by identity (what it is), or by truth (how things are) [Fine,K] |
17277 | If mind supervenes on the physical, it may also explain the physical (and not vice versa) [Fine,K] |
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] |
19538 | Entailment is modelled in formal semantics as set inclusion (where 'mammals' contains 'cats') [Dougherty/Rysiew] |