109 ideas
14857 | The highest wisdom has the guise of simplicity [Nietzsche] |
14854 | Deep thinkers know that they are always wrong [Nietzsche] |
14833 | Comedy is a transition from fear to exuberance [Nietzsche] |
14853 | Truth finds fewest champions not when it is dangerous, but when it is boring [Nietzsche] |
24075 | Convictions, more than lies, are the great enemy of truth [Nietzsche] |
9535 | 'Contradictory' propositions always differ in truth-value [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] |
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] |
9514 | If A and B are 'interderivable' from one another we may write A -||- B [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] |
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] |
9530 | A wff is 'contingent' if produces at least one T and at least one F [Lemmon] |
9517 | The 'scope' of a connective is the connective, the linked formulae, and the brackets [Lemmon] |
9529 | A wff is 'inconsistent' if all assignments to variables result in the value F [Lemmon] |
9519 | A 'substitution-instance' is a wff formed by consistent replacing variables with wffs [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] |
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] |
9394 | MPP: Given A and A→B, we may derive B [Lemmon] |
9397 | CP: Given a proof of B from A as assumption, we may derive A→B [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] |
9401 | ∨E: Derive C from A∨B, if C can be derived both from A and from B [Lemmon] |
9398 | ∧I: Given A and B, we may derive A∧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] |
9396 | DN: Given A, we may derive ¬¬A [Lemmon] |
9400 | ∨I: Given either A or B separately, we may derive A∨B [Lemmon] |
9522 | 'Modus ponendo tollens' (MPT) says P, ¬(P ∧ Q) |- ¬Q [Lemmon] |
9521 | 'Modus tollendo ponens' (MTP) 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] |
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] |
14858 | Being certain presumes that there are absolute truths, and means of arriving at them [Nietzsche] |
2614 | Modern phenomenalism holds that objects are logical constructions out of sense-data [Ayer] |
2615 | The concept of sense-data allows us to discuss appearances without worrying about reality [Ayer] |
14830 | Intuition only recognises what is possible, not what exists or is certain [Nietzsche] |
20378 | Just as skin hides the horrors of the body, vanity conceals the passions of the soul [Nietzsche] |
14820 | People always do what they think is right, according to the degree of their intellect [Nietzsche] |
14856 | Our judgment seems to cause our nature, but actually judgment arises from our nature [Nietzsche] |
14842 | Why are the strong tastes of other people so contagious? [Nietzsche] |
14835 | Artists are not especially passionate, but they pretend to be [Nietzsche] |
14807 | The history of morality rests on an error called 'responsibility', which rests on an error called 'free will' [Nietzsche] |
14823 | Ceasing to believe in human responsibility is bitter, if you had based the nobility of humanity on it [Nietzsche] |
14824 | It is absurd to blame nature and necessity; we should no more praise actions than we praise plants or artworks [Nietzsche] |
22473 | Nietzsche said the will doesn't exist, so it can't ground moral responsibility [Nietzsche, by Foot] |
14812 | Intellect is tied to morality, because it requires good memory and powerful imagination [Nietzsche] |
14810 | Originally it was the rulers who requited good for good and evil for evil who were called 'good' [Nietzsche] |
14831 | No one has ever done anything that was entirely for other people [Nietzsche] |
14855 | Simultaneous love and respect are impossible; love has no separation or rank, but respect admits power [Nietzsche] |
14815 | We get enormous pleasure from tales of noble actions [Nietzsche] |
14849 | We can only achieve happy moments, not happy eras [Nietzsche] |
14818 | First morality is force, then custom, then acceptance, then instinct, then a pleasure - and finally 'virtue' [Nietzsche] |
20103 | You are mastered by your own virtues, but you must master them, and turn them into tools [Nietzsche] |
14817 | The 'good' man does the moral thing as if by nature, easily and gladly, after a long inheritance [Nietzsche] |
14809 | All societies of good men give a priority to gratitude [Nietzsche] |
14816 | Justice (fairness) originates among roughly equal powers (as the Melian dialogues show) [Nietzsche] |
20112 | Pity consoles those who suffer, because they see that they still have the power to hurt [Nietzsche] |
14821 | Apart from philosophers, most people rightly have a low estimate of pity [Nietzsche] |
14841 | Many people are better at having good friends than being a good friend [Nietzsche] |
14843 | Women can be friends with men, but only some physical antipathy will maintain it [Nietzsche] |
14811 | In Homer it is the contemptible person, not the harmful person, who is bad [Nietzsche] |
20111 | We could live more naturally, relishing the spectacle, and not thinking we are special [Nietzsche] |
14844 | People do not experience boredom if they have never learned to work properly [Nietzsche] |
14808 | Over huge periods of time human character would change endlessly [Nietzsche] |
14822 | If self-defence is moral, then so are most expressions of 'immoral' egoism [Nietzsche] |
14838 | The state aims to protect individuals from one another [Nietzsche] |
14852 | Culture cannot do without passions and vices [Nietzsche] |
14846 | If we want the good life for the greatest number, we must let them decide on the good life [Nietzsche] |
14819 | Slavery cannot be judged by our standards, because the sense of justice was then less developed [Nietzsche] |
14847 | Laws that are well thought out, or laws that are easy to understand? [Nietzsche] |
14814 | Execution is worse than murder, because we are using the victim, and really we are the guilty [Nietzsche] |
14836 | People will enthusiastically pursue an unwanted war, once sacrifices have been made [Nietzsche] |
14845 | Don't crush girls with dull Gymnasium education, the way we have crushed boys! [Nietzsche] |
14839 | Interest in education gains strength when we lose interest in God [Nietzsche] |
14848 | Education in large states is mediocre, like cooking in large kitchens [Nietzsche] |
14834 | Teachers only gather knowledge for their pupils, and can't be serious about themselves [Nietzsche] |
14825 | In religious thought nature is a complex of arbitrary acts by conscious beings [Nietzsche] |
14826 | Modern man wants laws of nature in order to submit to them [Nietzsche] |
14827 | The Greeks saw the gods not as their masters, but as idealised versions of themselves [Nietzsche] |
14813 | Science rejecting the teaching of Christianity in favour of Epicurus shows the superiority of the latter [Nietzsche] |
14832 | The Sermon on the Mount is vanity - praying to one part of oneself, and demonising the rest [Nietzsche] |
14850 | Christ was the noblest human being [Nietzsche] |
14837 | Christ seems warm hearted, and suppressed intellect in favour of the intellectually weak [Nietzsche] |
14828 | Religion is tempting if your life is boring, but you can't therefore impose it on the busy people [Nietzsche] |