3 ideas
15927 | Definition just needs negation, known variables, conjunction, disjunction, substitution and quantification [Weyl, by Lavine] |
10121 | Contradiction is not a sign of falsity, nor lack of contradiction a sign of truth [Pascal] |
19347 | Substance needs independence, unity, and stability (for individuation); also it is a subject, for predicates [Perkins] |