100 ideas
| 22659 | It is wisdom to believe what you desire, because belief is needed to achieve it [James] |
| 22657 | All good philosophers start from a dumb conviction about which truths can be revealed [James] |
| 22647 | A complete system is just a classification of the whole world's ingredients [James] |
| 22648 | A single explanation must have a single point of view [James] |
| 22642 | Man has an intense natural interest in the consistency of his own thinking [James] |
| 22644 | Our greatest pleasure is the economy of reducing chaotic facts to one single fact [James] |
| 6710 | You can only define a statement that something is 'true' by referring to its functional possibilities [James] |
| 18986 | Truth is just a name for verification-processes [James] |
| 18983 | In many cases there is no obvious way in which ideas can agree with their object [James] |
| 18972 | Ideas are true in so far as they co-ordinate our experiences [James] |
| 18973 | New opinions count as 'true' if they are assimilated to an individual's current beliefs [James] |
| 18984 | True ideas are those we can assimilate, validate, corroborate and verify (and false otherwise) [James] |
| 22305 | If the hypothesis of God is widely successful, it is true [James] |
| 9535 | 'Contradictory' propositions always differ in truth-value [Lemmon] |
| 9511 | We write the conditional 'if P (antecedent) then Q (consequent)' as P→Q [Lemmon] |
| 9510 | That proposition that either P or Q is their 'disjunction', written P∨Q [Lemmon] |
| 9509 | That proposition that both P and Q is their 'conjunction', written P∧Q [Lemmon] |
| 9508 | The sign |- may be read as 'therefore' [Lemmon] |
| 9512 | We write the 'negation' of P (not-P) as ¬ [Lemmon] |
| 9513 | We write 'P if and only if Q' as P↔Q; it is also P iff Q, or (P→Q)∧(Q→P) [Lemmon] |
| 9514 | If A and B are 'interderivable' from one another we may write A -||- B [Lemmon] |
| 9516 | A 'well-formed formula' follows the rules for variables, ¬, →, ∧, ∨, and ↔ [Lemmon] |
| 9528 | A wff is a 'tautology' if all assignments to variables result in the value T [Lemmon] |
| 9518 | A 'theorem' is the conclusion of a provable sequent with zero assumptions [Lemmon] |
| 9519 | A 'substitution-instance' is a wff formed by consistent replacing variables with wffs [Lemmon] |
| 9529 | A wff is 'inconsistent' if all assignments to variables result in the value F [Lemmon] |
| 9531 | 'Contrary' propositions are never both true, so that ¬(A∧B) is a tautology [Lemmon] |
| 9534 | Two propositions are 'equivalent' if they mirror one another's truth-value [Lemmon] |
| 9530 | A wff is 'contingent' if produces at least one T and at least one F [Lemmon] |
| 9532 | 'Subcontrary' propositions are never both false, so that A∨B is a tautology [Lemmon] |
| 9517 | The 'scope' of a connective is the connective, the linked formulae, and the brackets [Lemmon] |
| 9533 | A 'implies' B if B is true whenever A is true (so that A→B is tautologous) [Lemmon] |
| 9396 | DN: Given A, we may derive ¬¬A [Lemmon] |
| 9393 | A: we may assume any proposition at any stage [Lemmon] |
| 9399 | ∧E: Given A∧B, we may derive either A or B separately [Lemmon] |
| 9398 | ∧I: Given A and B, we may derive A∧B [Lemmon] |
| 9397 | CP: Given a proof of B from A as assumption, we may derive A→B [Lemmon] |
| 9394 | MPP: Given A and A→B, we may derive B [Lemmon] |
| 9401 | ∨E: Derive C from A∨B, if C can be derived both from A and from B [Lemmon] |
| 9402 | RAA: If assuming A will prove B∧¬B, then derive ¬A [Lemmon] |
| 9395 | MTT: Given ¬B and A→B, we derive ¬A [Lemmon] |
| 9400 | ∨I: Given either A or B separately, we may derive A∨B [Lemmon] |
| 9521 | 'Modus tollendo ponens' (MTP) says ¬P, P ∨ Q |- Q [Lemmon] |
| 9522 | 'Modus ponendo tollens' (MPT) says P, ¬(P ∧ Q) |- ¬Q [Lemmon] |
| 9525 | We can change conditionals into negated conjunctions with P→Q -||- ¬(P ∧ ¬Q) [Lemmon] |
| 9524 | We can change conditionals into disjunctions with P→Q -||- ¬P ∨ Q [Lemmon] |
| 9523 | De Morgan's Laws make negated conjunctions/disjunctions into non-negated disjunctions/conjunctions [Lemmon] |
| 9527 | The Distributive Laws can rearrange a pair of conjunctions or disjunctions [Lemmon] |
| 9526 | We can change conjunctions into negated conditionals with P→Q -||- ¬(P → ¬Q) [Lemmon] |
| 9537 | Truth-tables are good for showing invalidity [Lemmon] |
| 9538 | A truth-table test is entirely mechanical, but this won't work for more complex logic [Lemmon] |
| 9536 | If any of the nine rules of propositional logic are applied to tautologies, the result is a tautology [Lemmon] |
| 9539 | Propositional logic is complete, since all of its tautologous sequents are derivable [Lemmon] |
| 13909 | Write '(∀x)(...)' to mean 'take any x: then...', and '(∃x)(...)' to mean 'there is an x such that....' [Lemmon] |
| 13902 | 'Gm' says m has property G, and 'Pmn' says m has relation P to n [Lemmon] |
| 13911 | The 'symbols' are bracket, connective, term, variable, predicate letter, reverse-E [Lemmon] |
| 13910 | Our notation uses 'predicate-letters' (for 'properties'), 'variables', 'proper names', 'connectives' and 'quantifiers' [Lemmon] |
| 13904 | Universal Elimination (UE) lets us infer that an object has F, from all things having F [Lemmon] |
| 13906 | With finite named objects, we can generalise with &-Intro, but otherwise we need ∀-Intro [Lemmon] |
| 13908 | UE all-to-one; UI one-to-all; EI arbitrary-to-one; EE proof-to-one [Lemmon] |
| 13901 | Predicate logic uses propositional connectives and variables, plus new introduction and elimination rules [Lemmon] |
| 13903 | Universal elimination if you start with the universal, introduction if you want to end with it [Lemmon] |
| 13905 | If there is a finite domain and all objects have names, complex conjunctions can replace universal quantifiers [Lemmon] |
| 13900 | 'Some Frenchmen are generous' is rendered by (∃x)(Fx→Gx), and not with the conditional → [Lemmon] |
| 9520 | The paradoxes of material implication are P |- Q → P, and ¬P |- P → Q [Lemmon] |
| 13007 | Archimedes defined a straight line as the shortest distance between two points [Archimedes, by Leibniz] |
| 22641 | Realities just are, and beliefs are true of them [James] |
| 22649 | Classification can only ever be for a particular purpose [James] |
| 18987 | A 'thing' is simply carved out of reality for human purposes [James] |
| 18981 | 'Substance' is just a word for groupings and structures in experience [James] |
| 18974 | Truth is a species of good, being whatever proves itself good in the way of belief [James] |
| 18989 | Pragmatism accepts any hypothesis which has useful consequences [James] |
| 22640 | We find satisfaction in consistency of all of our beliefs, perceptions and mental connections [James] |
| 22655 | Scientific genius extracts more than other people from the same evidence [James] |
| 22658 | Experimenters assume the theory is true, and stick to it as long as result don't disappoint [James] |
| 18971 | Theories are practical tools for progress, not answers to enigmas [James] |
| 18985 | True thoughts are just valuable instruments of action [James] |
| 18982 | Pragmatism says all theories are instrumental - that is, mental modes of adaptation to reality [James] |
| 22654 | We can't know if the laws of nature are stable, but we must postulate it or assume it [James] |
| 22656 | Trying to assess probabilities by mere calculation is absurd and impossible [James] |
| 22646 | We have a passion for knowing the parts of something, rather than the whole [James] |
| 22652 | The mind has evolved entirely for practical interests, seen in our reflex actions [James] |
| 22651 | Dogs' curiosity only concerns what will happen next [James] |
| 9286 | Consciousness is not a stuff, but is explained by the relations between experiences [James] |
| 9285 | 'Consciousness' is a nonentity, a mere echo of the disappearing 'soul' [James] |
| 23981 | Rage is inconceivable without bodily responses; so there are no disembodied emotions [James] |
| 22650 | How can the ground of rationality be itself rational? [James] |
| 22643 | It seems that we feel rational when we detect no irrationality [James] |
| 18975 | We return to experience with concepts, where they show us differences [James] |
| 22660 | Evolution suggests prevailing or survival as a new criterion of right and wrong [James] |
| 6570 | Imagine millions made happy on condition that one person suffers endless lonely torture [James] |
| 22645 | Understanding by means of causes is useless if they are not reduced to a minimum number [James] |
| 18980 | If there is a 'greatest knower', it doesn't follow that they know absolutely everything [James] |
| 18978 | It is hard to grasp a cosmic mind which produces such a mixture of goods and evils [James] |
| 18991 | If the God hypothesis works well, then it is true [James] |
| 18977 | The wonderful design of a woodpecker looks diabolical to its victims [James] |
| 18979 | Things with parts always have some structure, so they always appear to be designed [James] |
| 18976 | Private experience is the main evidence for God [James] |
| 22653 | Early Christianity says God recognises the neglected weak and tender impulses [James] |
| 18990 | Nirvana means safety from sense experience, and hindus and buddhists are just afraid of life [James] |