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All the ideas for 'What is Logic?st1=Ian Hacking', 'How to Define Theoretical Terms' and 'Internal and External Reasons'

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18 ideas

2. Reason / D. Definition / 2. Aims of Definition
15527 Defining terms either enables elimination, or shows that they don't require elimination [Lewis]
2. Reason / D. Definition / 3. Types of Definition
13838 A decent modern definition should always imply a semantics [Hacking]
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 / 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]
10. Modality / E. Possible worlds / 3. Transworld Objects / b. Rigid designation
15530 A logically determinate name names the same thing in every possible world [Lewis]
14. Science / B. Scientific Theories / 8. Ramsey Sentences
15531 The Ramsey sentence of a theory says that it has at least one realisation [Lewis]
15528 A Ramsey sentence just asserts that a theory can be realised, without saying by what [Lewis]
15526 There is a method for defining new scientific terms just using the terms we already understand [Lewis]
15529 It is better to have one realisation of a theory than many - but it may not always be possible [Lewis]
20. Action / C. Motives for Action / 3. Acting on Reason / c. Reasons as causes
9284 Reasons are 'internal' if they give a person a motive to act, but 'external' otherwise [Williams,B]