14 ideas
| 13201 | ∈ says the whole set is in the other; ⊆ says the members of the subset are in the other [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] |
| 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] |
| 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] |
| 9390 | Logic guides thinking, but it isn't a substitute for it [Rumfitt] |
| 9389 | Vague membership of sets is possible if the set is defined by its concept, not its members [Rumfitt] |
| 23633 | Many truths seem obvious, and point to universal agreement - which is what we find [Reid] |
| 23630 | Only philosophers treat ideas as objects [Reid] |
| 23629 | The ambiguity of words impedes the advancement of knowledge [Reid] |
| 23632 | Similar effects come from similar causes, and causes are only what are sufficient for the effects [Reid] |