98 ideas
23350 | A wise philosophers uses reason to cautiously judge each aspect of living [Epictetus] |
23355 | The task of philosophy is to establish standards, as occurs with weights and measures [Epictetus] |
21394 | Philosophy is knowing each logos, how they fit together, and what follows from them [Epictetus] |
23367 | Even pointing a finger should only be done for a reason [Epictetus] |
20876 | Philosophy investigates the causes of disagreements, and seeks a standard for settling them [Epictetus] |
21373 | We become objective when we detach ourselves from the world [Janaway] |
23344 | Reason itself must be compounded from some of our impressions [Epictetus] |
23343 | Because reason performs all analysis, we should analyse reason - but how? [Epictetus] |
9535 | 'Contradictory' propositions always differ in truth-value [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] |
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] |
9510 | That proposition that either P or Q is their 'disjunction', 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] |
9516 | A 'well-formed formula' follows the rules for variables, ¬, →, ∧, ∨, and ↔ [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] |
9534 | Two propositions are 'equivalent' if they mirror one another's truth-value [Lemmon] |
9517 | The 'scope' of a connective is the connective, the linked formulae, and the brackets [Lemmon] |
9518 | A 'theorem' is the conclusion of a provable sequent with zero assumptions [Lemmon] |
9533 | A 'implies' B if B is true whenever A is true (so that A→B is tautologous) [Lemmon] |
9532 | 'Subcontrary' propositions are never both false, so that A∨B is a tautology [Lemmon] |
9531 | 'Contrary' propositions are never both true, so that ¬(A∧B) is a tautology [Lemmon] |
9528 | A wff is a 'tautology' if all assignments to variables result in the value T [Lemmon] |
9530 | A wff is 'contingent' if produces at least one T and at least one F [Lemmon] |
9396 | DN: Given A, we may derive ¬¬A [Lemmon] |
9398 | ∧I: Given A and B, we may derive A∧B [Lemmon] |
9394 | MPP: Given A and A→B, we may derive B [Lemmon] |
9399 | ∧E: Given A∧B, we may derive either A or B separately [Lemmon] |
9401 | ∨E: Derive C from A∨B, if C can be derived both from A and from B [Lemmon] |
9395 | MTT: Given ¬B and A→B, we derive ¬A [Lemmon] |
9393 | A: we may assume any proposition at any stage [Lemmon] |
9400 | ∨I: Given either A or B separately, we may derive A∨B [Lemmon] |
9402 | RAA: If assuming A will prove B∧¬B, then derive ¬A [Lemmon] |
9397 | CP: Given a proof of B from A as assumption, we may derive A→B [Lemmon] |
9522 | 'Modus ponendo tollens' (MPT) says P, ¬(P ∧ Q) |- ¬Q [Lemmon] |
9526 | We can change conjunctions into negated conditionals with P→Q -||- ¬(P → ¬Q) [Lemmon] |
9527 | The Distributive Laws can rearrange a pair of conjunctions or disjunctions [Lemmon] |
9523 | De Morgan's Laws make negated conjunctions/disjunctions into non-negated disjunctions/conjunctions [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] |
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] |
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] |
9520 | The paradoxes of material implication are P |- Q → P, and ¬P |- P → Q [Lemmon] |
23359 | We can't believe apparent falsehoods, or deny apparent truths [Epictetus] |
23356 | Self-evidence is most obvious when people who deny a proposition still have to use it [Epictetus] |
23330 | Freedom is making all things happen by choice, without constraint [Epictetus] |
23342 | Freedom is acting by choice, with no constraint possible [Epictetus] |
23329 | We make progress when we improve and naturalise our choices, asserting their freedom [Epictetus] |
23332 | Zeus gave me a nature which is free (like himself) from all compulsion [Epictetus] |
23331 | Not even Zeus can control what I choose [Epictetus] |
23338 | You can fetter my leg, but not even Zeus can control my power of choice [Epictetus] |
20875 | If we could foresee the future, we should collaborate with disease and death [Epictetus] |
23347 | If I know I am fated to be ill, I should want to be ill [Epictetus] |
23325 | Epictetus developed a notion of will as the source of our responsibility [Epictetus, by Frede,M] |
20873 | Tragedies are versified sufferings of people impressed by externals [Epictetus] |
23364 | Homer wrote to show that the most blessed men can be ruined by poor judgement [Epictetus] |
23340 | We consist of animal bodies and god-like reason [Epictetus] |
23366 | We see nature's will in the ways all people are the same [Epictetus] |
23358 | Every species produces exceptional beings, and we must just accept their nature [Epictetus] |
23339 | I will die as becomes a person returning what he does not own [Epictetus] |
23345 | Don't be frightened of pain or death; only be frightened of fearing them [Epictetus] |
23357 | Knowledge of what is good leads to love; only the wise, who distinguish good from evil, can love [Epictetus] |
23363 | The evil for everything is what is contrary to its nature [Epictetus] |
23328 | The essences of good and evil are in dispositions to choose [Epictetus] |
23362 | All human ills result from failure to apply preconceptions to particular cases [Epictetus] |
23353 | We have a natural sense of honour [Epictetus] |
23354 | If someone harms themselves in harming me, then I harm myself by returning the harm [Epictetus] |
23324 | In the Discourses choice [prohairesis] defines our character and behaviour [Epictetus, by Frede,M] |
4022 | Epictetus says we should console others for misfortune, but not be moved by pity [Epictetus, by Taylor,C] |
23365 | If someone is weeping, you should sympathise and help, but not share his suffering [Epictetus] |
23361 | Health is only a good when it is used well [Epictetus] |
23346 | A person is as naturally a part of a city as a foot is part of the body [Epictetus] |
23351 | We are citizens of the universe, and principal parts of it [Epictetus] |
23352 | A citizen should only consider what is good for the whole society [Epictetus] |
20874 | A citizen is committed to ignore private advantage, and seek communal good [Epictetus] |
22604 | Punishing a criminal for moral ignorance is the same as punishing someone for being blind [Epictetus] |
23368 | Perhaps we should persuade culprits that their punishment is just? [Epictetus] |
23349 | Asses are born to carry human burdens, not as ends in themselves [Epictetus] |
23341 | God created humans as spectators and interpreters of God's works [Epictetus] |
23348 | Both god and the good bring benefits, so their true nature seems to be the same [Epictetus] |
23360 | Each of the four elements in you is entirely scattered after death [Epictetus] |