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All the ideas for 'What is Logic?st1=Ian Hacking', 'The Discourses' and 'Against the Professors (six books)'

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18 ideas

2. Reason / D. Definition / 3. Types of Definition
13838 A decent modern definition should always imply a semantics [Hacking]
3. Truth / A. Truth Problems / 5. Truth Bearers
6021 It is only when we say a proposition that we speak truly or falsely [Sext.Empiricus]
4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / d. Basic theorems of PL
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]
5. Theory of Logic / A. Overview of Logic / 4. Pure Logic
13845 The various logics are abstractions made from terms like 'if...then' in English [Hacking]
5. Theory of Logic / A. Overview of Logic / 5. First-Order Logic
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]
5. Theory of Logic / A. Overview of Logic / 7. Second-Order Logic
13842 Second-order completeness seems to need intensional entities and possible worlds [Hacking]
5. Theory of Logic / E. Structures of Logic / 1. Logical Form
6020 'Man is a rational mortal animal' is equivalent to 'if something is a man, that thing is a rational mortal animal' [Sext.Empiricus]
5. Theory of Logic / E. Structures of Logic / 2. Logical Connectives / a. Logical connectives
13837 With a pure notion of truth and consequence, the meanings of connectives are fixed syntactically [Hacking]
5. Theory of Logic / E. Structures of Logic / 4. Variables in Logic
13839 Perhaps variables could be dispensed with, by arrows joining places in the scope of quantifiers [Hacking]
5. Theory of Logic / J. Model Theory in Logic / 3. Löwenheim-Skolem Theorems
13843 If it is a logic, the Löwenheim-Skolem theorem holds for it [Hacking]
14. Science / A. Basis of Science / 1. Observation
6026 How can you investigate without some preconception of your object? [Sext.Empiricus]
23. Ethics / B. Contract Ethics / 9. Contractualism
6032 Right actions, once done, are those with a reasonable justification [Sext.Empiricus]
25. Social Practice / E. Policies / 2. Religion in Society
19813 All legislators invoke God in support of extraordinary laws, because their justification is not obvious [Machiavelli]
7126 Rulers should preserve the foundations of religion, to ensure good behaviour and unity [Machiavelli]
26. Natural Theory / A. Speculations on Nature / 4. Mathematical Nature
1517 The tektraktys (1+2+3+4=10) is the 'fount of ever-flowing nature' [Sext.Empiricus]