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All the ideas for 'What is Logic?st1=Ian Hacking', 'Treatise of Freewill' and 'The Condemnation of 1277'

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17 ideas

2. Reason / D. Definition / 3. Types of Definition
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
'Thinning' ('dilution') is the key difference between deduction (which allows it) and induction [Hacking]
Gentzen's Cut Rule (or transitivity of deduction) is 'If A |- B and B |- C, then A |- C' [Hacking]
Only Cut reduces complexity, so logic is constructive without it, and it can be dispensed with [Hacking]
5. Theory of Logic / A. Overview of Logic / 4. Pure Logic
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
First-order logic is the strongest complete compact theory with Löwenheim-Skolem [Hacking]
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
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
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
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
If it is a logic, the Löwenheim-Skolem theorem holds for it [Hacking]
10. Modality / B. Possibility / 1. Possibility
In future, only logical limits can be placed on divine omnipotence [Anon (Par), by Boulter]
13. Knowledge Criteria / B. Internal Justification / 4. Foundationalism / f. Foundationalism critique
It is heresy to require self-evident foundational principles in order to be certain [Anon (Par)]
23. Ethics / F. Existentialism / 6. Authentic Self
There is a self-determing power in each person, which makes them what they are [Cudworth]
25. Social Practice / E. Policies / 5. Education / d. Study of history
It is heresy to teach that history repeats every 36,000 years [Anon (Par)]
28. God / A. Divine Nature / 3. Divine Perfections
It is heresy to teach that natural impossibilities cannot even be achieved by God [Anon (Par)]
28. God / B. Proving God / 2. Proofs of Reason / b. Ontological Proof critique
It is heresy to teach that we can know God by his essence in this mortal life [Anon (Par)]