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All the ideas for 'What is Logic?st1=Ian Hacking', 'Tarski on Truth and Logical Consequence' and 'Modality'

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30 ideas

2. Reason / A. Nature of Reason / 1. On Reason
5750 Consistency is modal, saying propositions are consistent if they could be true together [Melia]
2. Reason / D. Definition / 3. Types of Definition
13838 A decent modern definition should always imply a semantics [Hacking]
3. Truth / F. Semantic Truth / 1. Tarski's Truth / c. Meta-language for truth
19323 'Snow is white' depends on meaning; whether snow is white depends on snow [Etchemendy]
3. Truth / G. Axiomatic Truth / 1. Axiomatic Truth
19137 We can get a substantive account of Tarski's truth by adding primitive 'true' to the object language [Etchemendy]
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]
4. Formal Logic / C. Predicate Calculus PC / 1. Predicate Calculus PC
5737 Predicate logic has connectives, quantifiers, variables, predicates, equality, names and brackets [Melia]
4. Formal Logic / D. Modal Logic ML / 1. Modal Logic
5744 First-order predicate calculus is extensional logic, but quantified modal logic is intensional (hence dubious) [Melia]
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 / G. Quantification / 5. Second-Order Quantification
5740 Second-order logic needs second-order variables and quantification into predicate position [Melia]
5. Theory of Logic / J. Model Theory in Logic / 1. Logical Models
5741 If every model that makes premises true also makes conclusion true, the argument is valid [Melia]
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 / D. Theories of Reality / 8. Facts / a. Facts
5736 No sort of plain language or levels of logic can express modal facts properly [Melia]
5735 Maybe names and predicates can capture any fact [Melia]
9. Objects / F. Identity among Objects / 7. Indiscernible Objects
5746 The Identity of Indiscernibles is contentious for qualities, and trivial for non-qualities [Melia]
10. Modality / A. Necessity / 2. Nature of Necessity
5738 We may be sure that P is necessary, but is it necessarily necessary? [Melia]
10. Modality / A. Necessity / 4. De re / De dicto modality
5732 'De re' modality is about things themselves, 'de dicto' modality is about propositions [Melia]
10. Modality / B. Possibility / 1. Possibility
5739 Sometimes we want to specify in what ways a thing is possible [Melia]
10. Modality / E. Possible worlds / 1. Possible Worlds / a. Possible worlds
5734 Possible worlds make it possible to define necessity and counterfactuals without new primitives [Melia]
5742 In possible worlds semantics the modal operators are treated as quantifiers [Melia]
5743 If possible worlds semantics is not realist about possible worlds, logic becomes merely formal [Melia]
5749 Possible worlds could be real as mathematics, propositions, properties, or like books [Melia]
10. Modality / E. Possible worlds / 2. Nature of Possible Worlds / b. Worlds as fictions
5751 The truth of propositions at possible worlds are implied by the world, just as in books [Melia]
19. Language / A. Nature of Meaning / 5. Meaning as Verification
5748 We accept unverifiable propositions because of simplicity, utility, explanation and plausibility [Melia]