66 ideas
| 23027 | Ideals and metaphysics are practical, not imaginative or speculative [Green,TH, by Muirhead] |
| 23030 | Truth is a relation to a whole of organised knowledge in the collection of rational minds [Green,TH, by Muirhead] |
| 9724 | Until the 1960s the only semantics was truth-tables [Enderton] |
| 9703 | 'dom R' indicates the 'domain' of objects having a relation [Enderton] |
| 9705 | 'fld R' indicates the 'field' of all objects in the relation [Enderton] |
| 9704 | 'ran R' indicates the 'range' of objects being related to [Enderton] |
| 9710 | We write F:A→B to indicate that A maps into B (the output of F on A is in B) [Enderton] |
| 9707 | 'F(x)' is the unique value which F assumes for a value of x [Enderton] |
| 13201 | ∈ says the whole set is in the other; ⊆ says the members of the subset are in the other [Enderton] |
| 9712 | A relation is 'symmetric' on a set if every ordered pair has the relation in both directions [Enderton] |
| 9713 | A relation is 'transitive' if it can be carried over from two ordered pairs to a third [Enderton] |
| 13204 | The 'ordered pair' <x,y> is defined to be {{x}, {x,y}} [Enderton] |
| 13206 | A 'linear or total ordering' must be transitive and satisfy trichotomy [Enderton] |
| 9699 | The 'powerset' of a set is all the subsets of a given set [Enderton] |
| 9700 | Two sets are 'disjoint' iff their intersection is empty [Enderton] |
| 9702 | A 'domain' of a relation is the set of members of ordered pairs in the relation [Enderton] |
| 9701 | A 'relation' is a set of ordered pairs [Enderton] |
| 9706 | A 'function' is a relation in which each object is related to just one other object [Enderton] |
| 9708 | A function 'maps A into B' if the relating things are set A, and the things related to are all in B [Enderton] |
| 9709 | A function 'maps A onto B' if the relating things are set A, and the things related to are set B [Enderton] |
| 9711 | A relation is 'reflexive' on a set if every member bears the relation to itself [Enderton] |
| 9714 | A relation satisfies 'trichotomy' if all pairs are either relations, or contain identical objects [Enderton] |
| 9717 | A set is 'dominated' by another if a one-to-one function maps the first set into a subset of the second [Enderton] |
| 13200 | Note that {Φ} =/= Φ, because Φ ∈ {Φ} but Φ ∉ Φ [Enderton] |
| 13199 | The empty set may look pointless, but many sets can be constructed from it [Enderton] |
| 13203 | The singleton is defined using the pairing axiom (as {x,x}) [Enderton] |
| 9715 | An 'equivalence relation' is a reflexive, symmetric and transitive binary relation [Enderton] |
| 9716 | We 'partition' a set into distinct subsets, according to each relation on its objects [Enderton] |
| 13202 | Fraenkel added Replacement, to give a theory of ordinal numbers [Enderton] |
| 13205 | We can only define functions if Choice tells us which items are involved [Enderton] |
| 9722 | Inference not from content, but from the fact that it was said, is 'conversational implicature' [Enderton] |
| 9718 | Validity is either semantic (what preserves truth), or proof-theoretic (following procedures) [Enderton] |
| 9721 | A logical truth or tautology is a logical consequence of the empty set [Enderton] |
| 9994 | A truth assignment to the components of a wff 'satisfy' it if the wff is then True [Enderton] |
| 9719 | A proof theory is 'sound' if its valid inferences entail semantic validity [Enderton] |
| 9720 | A proof theory is 'complete' if semantically valid inferences entail proof-theoretic validity [Enderton] |
| 9995 | Proof in finite subsets is sufficient for proof in an infinite set [Enderton] |
| 9996 | Expressions are 'decidable' if inclusion in them (or not) can be proved [Enderton] |
| 9997 | For a reasonable language, the set of valid wff's can always be enumerated [Enderton] |
| 9723 | Sentences with 'if' are only conditionals if they can read as A-implies-B [Enderton] |
| 23044 | All knowledge rests on a fundamental unity between the knower and what is known [Green,TH, by Muirhead] |
| 23034 | The ultimate test for truth is the systematic interdependence in nature [Green,TH, by Muirhead] |
| 23029 | Knowledge is secured by the relations between its parts, through differences and identities [Green,TH, by Muirhead] |
| 468 | Musical performance can reveal a range of virtues [Damon of Ath.] |
| 23035 | The good life aims at perfections, or absolute laws, or what is absolutely desirable [Green,TH] |
| 23032 | What is distinctive of human life is the desire for self-improvement [Green,TH, by Muirhead] |
| 23033 | Hedonism offers no satisfaction, because what we desire is self-betterment [Green,TH, by Muirhead] |
| 23046 | States only have full authority if they heed the claims of human fellowship [Green,TH] |
| 23045 | Politics is compromises, which seem supported by a social contract, but express the will of no one [Green,TH] |
| 23050 | The ideal is a society in which all citizens are ladies and gentlemen [Green,TH] |
| 23052 | Enfranchisement is an end in itself; it makes a person moral, and gives a basis for respect [Green,TH] |
| 23036 | The good is identified by the capacities of its participants [Green,TH, by Muirhead] |
| 23039 | A true state is only unified and stabilised by acknowledging individuality [Green,TH, by Muirhead] |
| 23037 | People are improved by egalitarian institutions and habits [Green,TH] |
| 23051 | Equality also implies liberty, because equality must be of opportunity as well as possessions [Green,TH] |
| 23043 | All talk of the progress of a nation must reduce to the progress of its individual members [Green,TH] |
| 23038 | People only develop their personality through co-operation with the social whole [Green,TH, by Muirhead] |
| 23028 | The highest political efforts express our deeper social spirit [Green,TH, by Muirhead] |
| 23054 | Communism is wrong because it restricts the freedom of individuals to contribute to the community [Green,TH, by Muirhead] |
| 23047 | Original common ownership is securing private property, not denying it [Green,TH, by Muirhead] |
| 23042 | National spirit only exists in the individuals who embody it [Green,TH, by Muirhead] |
| 23048 | The ground of property ownership is not force but the power to use it for social ends [Green,TH, by Muirhead] |
| 23049 | Property is needed by all citizens, to empower them to achieve social goods [Green,TH] |
| 23040 | If something develops, its true nature is embodied in its end [Green,TH] |
| 23031 | God is the ideal end of the mature mind's final development [Green,TH] |
| 23041 | God is the realisation of the possibilities of each man's self [Green,TH] |