Combining Texts

All the ideas for 'What is Logic?st1=Ian Hacking', 'Identity in Substances and True Propositions' and 'Propositional Objects'

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16 ideas

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]
7. Existence / C. Structure of Existence / 6. Fundamentals / c. Monads
19405 Substances are in harmony, because they each express the one reality in themselves [Leibniz]
11. Knowledge Aims / A. Knowledge / 4. Belief / e. Belief holism
18969 How do you distinguish three beliefs from four beliefs or two beliefs? [Quine]
19. Language / D. Propositions / 2. Abstract Propositions / a. Propositions as sense
18967 A 'proposition' is said to be the timeless cognitive part of the meaning of a sentence [Quine]
19. Language / D. Propositions / 6. Propositions Critique
18968 The problem with propositions is their individuation. When do two sentences express one proposition? [Quine]
27. Natural Reality / C. Space / 3. Points in Space
18970 The concept of a 'point' makes no sense without the idea of absolute position [Quine]