75 ideas
18915 | If facts are the truthmakers, they are not in the world [Engelbretsen] |
18919 | There are no 'falsifying' facts, only an absence of truthmakers [Engelbretsen] |
18913 | Traditional term logic struggled to express relations [Engelbretsen] |
18907 | Term logic rests on negated terms or denial, and that propositions are tied pairs [Engelbretsen] |
9535 | 'Contradictory' propositions always differ in truth-value [Lemmon] |
9514 | If A and B are 'interderivable' from one another we may write A -||- B [Lemmon] |
9511 | We write the conditional 'if P (antecedent) then Q (consequent)' as P→Q [Lemmon] |
9512 | We write the 'negation' of P (not-P) as ¬ [Lemmon] |
9508 | The sign |- may be read as 'therefore' [Lemmon] |
9509 | That proposition that both P and Q is their 'conjunction', written P∧Q [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] |
9510 | That proposition that either P or Q is their 'disjunction', written P∨Q [Lemmon] |
9517 | The 'scope' of a connective is the connective, the linked formulae, and the brackets [Lemmon] |
9519 | A 'substitution-instance' is a wff formed by consistent replacing variables with wffs [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] |
9534 | Two propositions are 'equivalent' if they mirror one another's truth-value [Lemmon] |
9518 | A 'theorem' is the conclusion of a provable sequent with zero assumptions [Lemmon] |
9528 | A wff is a 'tautology' if all assignments to variables result in the value T [Lemmon] |
9529 | A wff is 'inconsistent' if all assignments to variables result in the value F [Lemmon] |
9533 | A 'implies' B if B is true whenever A is true (so that A→B is tautologous) [Lemmon] |
9531 | 'Contrary' propositions are never both true, so that ¬(A∧B) is a tautology [Lemmon] |
9516 | A 'well-formed formula' follows the rules for variables, ¬, →, ∧, ∨, and ↔ [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] |
9397 | CP: Given a proof of B from A as assumption, we may derive A→B [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] |
9394 | MPP: Given A and A→B, we may derive B [Lemmon] |
9396 | DN: Given A, we may derive ¬¬A [Lemmon] |
9398 | ∧I: Given A and B, we may derive A∧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] |
9522 | 'Modus ponendo tollens' (MPT) says P, ¬(P ∧ Q) |- ¬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] |
9524 | We can change conditionals into disjunctions with P→Q -||- ¬P ∨ Q [Lemmon] |
9525 | We can change conditionals into negated conjunctions with P→Q -||- ¬(P ∧ ¬Q) [Lemmon] |
9521 | 'Modus tollendo ponens' (MTP) says ¬P, P ∨ Q |- Q [Lemmon] |
9526 | We can change conjunctions into negated conditionals with P→Q -||- ¬(P → ¬Q) [Lemmon] |
9538 | A truth-table test is entirely mechanical, but this won't work for more complex logic [Lemmon] |
9537 | Truth-tables are good for showing invalidity [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] |
13911 | The 'symbols' are bracket, connective, term, variable, predicate letter, reverse-E [Lemmon] |
13902 | 'Gm' says m has property G, and 'Pmn' says m has relation P to n [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] |
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] |
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] |
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] |
18912 | Was logic a branch of mathematics, or mathematics a branch of logic? [Engelbretsen] |
9520 | The paradoxes of material implication are P |- Q → P, and ¬P |- P → Q [Lemmon] |
18922 | Logical syntax is actually close to surface linguistic form [Engelbretsen] |
18905 | Propositions can be analysed as pairs of terms glued together by predication [Engelbretsen] |
18908 | Standard logic only negates sentences, even via negated general terms or predicates [Engelbretsen] |
18917 | Existence and nonexistence are characteristics of the world, not of objects [Engelbretsen] |
18916 | Facts are not in the world - they are properties of the world [Engelbretsen] |
18921 | Individuals are arranged in inclusion categories that match our semantics [Engelbretsen] |
7647 | The imagination alone perceives all objects; it is the soul, playing all its roles [La Mettrie] |
7645 | When falling asleep, the soul becomes paralysed and weak, just like the body [La Mettrie] |
23225 | The soul's faculties depend on the brain, and are simply the brain's organisation [La Mettrie] |
7652 | Man is a machine, and there exists only one substance, diversely modified [La Mettrie] |
7650 | All thought is feeling, and rationality is the sensitive soul contemplating reasoning [La Mettrie] |
7651 | With wonderful new machines being made, a speaking machine no longer seems impossible [La Mettrie] |
18918 | Terms denote objects with properties, and statements denote the world with that property [Engelbretsen] |
18920 | 'Socrates is wise' denotes a sentence; 'that Socrates is wise' denotes a proposition [Engelbretsen] |
18906 | Negating a predicate term and denying its unnegated version are quite different [Engelbretsen] |
7648 | The sun and rain weren't made for us; they sometimes burn us, or spoil our seeds [La Mettrie] |
7646 | There is no abrupt transition from man to animal; only language has opened a gap [La Mettrie] |
7649 | There is no clear idea of the soul, which should only refer to our thinking part [La Mettrie] |