90 ideas
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] |
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] |
9509 | That proposition that both P and Q is their 'conjunction', written P∧Q [Lemmon] |
9508 | The sign |- may be read as 'therefore' [Lemmon] |
9516 | A 'well-formed formula' follows the rules for variables, ¬, →, ∧, ∨, and ↔ [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] |
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] |
9533 | A 'implies' B if B is true whenever A is true (so that A→B is tautologous) [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] |
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] |
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] |
9401 | ∨E: Derive C from A∨B, if C can be derived both from A and from B [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] |
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] |
17644 | Metaphysical realism is committed to there being one ultimate true theory [Putnam] |
17648 | It is an illusion to think there could be one good scientific theory of reality [Putnam] |
17643 | Shape is essential relative to 'statue', but not essential relative to 'clay' [Putnam] |
4266 | Having beliefs involves recognition, expectation and surprise [Scruton] |
4265 | If an animal has beliefs, that implies not only that it can make mistakes, but that it can learn from them [Scruton] |
4264 | Perception (which involves an assessment) is a higher state than sensation [Scruton] |
17642 | The old view that sense data are independent of mind is quite dotty [Putnam] |
4271 | There is consciousness whenever behaviour must be explained in terms of mental activity [Scruton] |
4272 | Our concept of a person is derived from Roman law [Scruton] |
4267 | Conditioning may change behaviour without changing the mind [Scruton] |
4269 | An emotion is a motive which is also a feeling [Scruton] |
4270 | Do we use reason to distinguish people from animals, or use that difference to define reason? [Scruton] |
4284 | All moral life depends ultimately on piety, which is our recognition of our own dependence [Scruton] |
4273 | Kant's Moral Law is the rules rational beings would accept when trying to live by agreement [Scruton] |
4274 | The modern virtues are courage, prudence, wisdom, temperance, justice, charity and loyalty [Scruton] |
4286 | Only just people will drop their own self-interests when faced with an impartial verdict [Scruton] |
4283 | Sympathy can undermine the moral order just as much as crime does [Scruton] |
4290 | That which can only be done by a callous person, ought not to be done [Scruton] |
4285 | As soon as we drop self-interest and judge impartially, we find ourselves agreeing about conflicts [Scruton] |
4287 | Utilitarianism merely guides us (by means of sympathy) when the moral law is silent [Scruton] |
4282 | Morality is not a sort of calculation, it is what sets the limits to when calculation is appropriate [Scruton] |
4281 | Utilitarianism says we can't blame Stalin yet, but such a theory is a sick joke [Scruton] |
4280 | Utilitarianism is wrong precisely because it can't distinguish animals from people [Scruton] |
4296 | Brutal animal sports are banned because they harm the personality of the watcher [Scruton] |
4288 | Many breeds of animals have needs which our own ancestors planted in them [Scruton] |
4293 | Introducing a natural means of controlling animal population may not be very compassionate [Scruton] |
4295 | We favour our own animals over foreign ones because we see them as fellow citizens [Scruton] |
4268 | Animals command our sympathy and moral concern initially because of their intentionality [Scruton] |
4291 | Letting your dog kill wild rats, and keeping rats for your dog to kill, are very different [Scruton] |
4263 | Many of the stranger forms of life (e.g. worms) interest us only as a species, not as individuals [Scruton] |
4276 | An animal has individuality if it is nameable, and advanced animals can respond to their name [Scruton] |
4277 | I may avoid stepping on a spider or flower, but fellow-feeling makes me protect a rabbit [Scruton] |
4278 | Lucky animals are eaten by large predators, the less lucky starve, and worst is death by small predators [Scruton] |
4279 | We can easily remove the risk of suffering from an animal's life, but we shouldn't do it [Scruton] |
4289 | Sheep and cattle live comfortable lives, and die an enviably easy death [Scruton] |
4292 | Concern for one animal may harm the species, if the individual is part of a bigger problem [Scruton] |
4294 | Animals are outside the community of rights, but we still have duties towards them [Scruton] |
17645 | An alien might think oxygen was the main cause of a forest fire [Putnam] |