44 ideas
| 13838 | A decent modern definition should always imply a semantics [Hacking] |
| 13834 | Gentzen's Cut Rule (or transitivity of deduction) is 'If A |- B and B |- C, then A |- C' [Hacking] |
| 13835 | Only Cut reduces complexity, so logic is constructive without it, and it can be dispensed with [Hacking] |
| 13833 | 'Thinning' ('dilution') is the key difference between deduction (which allows it) and induction [Hacking] |
| 13845 | The various logics are abstractions made from terms like 'if...then' in English [Hacking] |
| 13840 | First-order logic is the strongest complete compact theory with Löwenheim-Skolem [Hacking] |
| 13844 | A limitation of first-order logic is that it cannot handle branching quantifiers [Hacking] |
| 13842 | Second-order completeness seems to need intensional entities and possible worlds [Hacking] |
| 14249 | Boolos reinterprets second-order logic as plural logic [Boolos, by Oliver/Smiley] |
| 10830 | Second-order logic metatheory is set-theoretic, and second-order validity has set-theoretic problems [Boolos] |
| 10829 | A sentence can't be a truth of logic if it asserts the existence of certain sets [Boolos] |
| 13837 | With a pure notion of truth and consequence, the meanings of connectives are fixed syntactically [Hacking] |
| 13839 | Perhaps variables could be dispensed with, by arrows joining places in the scope of quantifiers [Hacking] |
| 10832 | '∀x x=x' only means 'everything is identical to itself' if the range of 'everything' is fixed [Boolos] |
| 13843 | If it is a logic, the Löwenheim-Skolem theorem holds for it [Hacking] |
| 10834 | Weak completeness: if it is valid, it is provable. Strong: it is provable from a set of sentences [Boolos] |
| 13841 | Why should compactness be definitive of logic? [Boolos, by Hacking] |
| 10833 | Many concepts can only be expressed by second-order logic [Boolos] |
| 12747 | Monads are not extended, but have a kind of situation in extension [Leibniz] |
| 12748 | Only monads are substances, and bodies are collections of them [Leibniz] |
| 13184 | The division of nature into matter makes distinct appearances, and that presupposes substances [Leibniz] |
| 13188 | The only indications of reality are agreement among phenomena, and their agreement with necessities [Leibniz] |
| 12752 | Only unities have any reality [Leibniz] |
| 13187 | In actual things nothing is indefinite [Leibniz] |
| 19383 | A man's distant wife dying is a real change in him [Leibniz] |
| 13179 | A complete monad is a substance with primitive active and passive power [Leibniz] |
| 12749 | Derivate forces are in phenomena, but primitive forces are in the internal strivings of substances [Leibniz] |
| 12722 | Thought terminates in force, rather than extension [Leibniz] |
| 19379 | The law of the series, which determines future states of a substance, is what individuates it [Leibniz] |
| 13182 | Changeable accidents are modifications of unchanging essences [Leibniz] |
| 13178 | Things in different locations are different because they 'express' those locations [Leibniz] |
| 19412 | If two bodies only seem to differ in their position, those different environments will matter [Leibniz] |
| 19411 | In nature there aren't even two identical straight lines, so no two bodies are alike [Leibniz] |
| 19410 | Scientific truths are supported by mutual agreement, as well as agreement with the phenomena [Leibniz] |
| 13183 | Primitive forces are internal strivings of substances, acting according to their internal laws [Leibniz] |
| 19409 | Soul represents body, but soul remains unchanged, while body continuously changes [Leibniz] |
| 11873 | Our notions may be formed from concepts, but concepts are formed from things [Leibniz] |
| 13186 | Universals are just abstractions by concealing some of the circumstances [Leibniz] |
| 13185 | Even if extension is impenetrable, this still offers no explanation for motion and its laws [Leibniz] |
| 13177 | An entelechy is a law of the series of its event within some entity [Leibniz] |
| 13093 | The only permanence in things, constituting their substance, is a law of continuity [Leibniz] |
| 13096 | The force behind motion is like a soul, with its own laws of continual change [Leibniz] |
| 13180 | Space is the order of coexisting possibles [Leibniz] |
| 13181 | Time is the order of inconsistent possibilities [Leibniz] |