15 ideas
| 5035 | The two basics of reasoning are contradiction and sufficient reason [Leibniz] |
| 11022 | Gentzen introduced a natural deduction calculus (NK) in 1934 [Gentzen, by Read] |
| 11065 | The inferential role of a logical constant constitutes its meaning [Gentzen, by Hanna] |
| 11023 | The logical connectives are 'defined' by their introduction rules [Gentzen] |
| 11213 | Each logical symbol has an 'introduction' rule to define it, and hence an 'elimination' rule [Gentzen] |
| 10067 | Gentzen proved the consistency of arithmetic from assumptions beyond arithmetic [Gentzen, by Musgrave] |
| 11976 | Aristotelian essentialism says essences are not relative to specification [Lewis] |
| 11978 | Causal necessities hold in all worlds compatible with the laws of nature [Lewis] |
| 11979 | It doesn't take the whole of a possible Humphrey to win the election [Lewis] |
| 16994 | Counterpart theory is bizarre, as no one cares what happens to a mere counterpart [Kripke on Lewis] |
| 11974 | Counterparts are not the original thing, but resemble it more than other things do [Lewis] |
| 11975 | If the closest resembler to you is in fact quite unlike you, then you have no counterpart [Lewis] |
| 11977 | Essential attributes are those shared with all the counterparts [Lewis] |
| 5038 | Assume that mind and body follow their own laws, but God has harmonised them [Leibniz] |
| 5037 | God doesn't decide that Adam will sin, but that sinful Adam's existence is to be preferred [Leibniz] |