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3 ideas
13825 | Natural deduction introduction rules may represent 'definitions' of logical connectives [Prawitz] |
Full Idea: With Gentzen's natural deduction, we may say that the introductions represent, as it were, the 'definitions' of the logical constants. The introductions are not literally understood as 'definitions'. | |
From: Dag Prawitz (Gentzen's Analysis of First-Order Proofs [1974], 2.2.2) | |
A reaction: [Hacking, in 'What is Logic? §9' says Gentzen had the idea that his rules actually define the constants; not sure if Prawitz and Hacking are disagreeing] |
13696 | When a variable is 'free' of the quantifier, the result seems incapable of truth or falsity [Sider] |
Full Idea: When a variable is not combined with a quantifier (and so is 'free'), the result is, intuitively, semantically incomplete, and incapable of truth or falsity. | |
From: Theodore Sider (Logic for Philosophy [2010], 4.2) |
13700 | A 'total' function must always produce an output for a given domain [Sider] |
Full Idea: Calling a function a 'total' function 'over D' means that the function must have a well-defined output (which is a member of D) whenever it is given as inputs any n members of D. | |
From: Theodore Sider (Logic for Philosophy [2010], 5.2) |