Combining Texts

All the ideas for 'On Sufficient Reason', 'The Actual and the Possible' and 'On Second-Order Logic'

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10 ideas

2. Reason / B. Laws of Thought / 1. Laws of Thought
19404 Necessities rest on contradiction, and contingencies on sufficient reason [Leibniz]
5. Theory of Logic / A. Overview of Logic / 7. Second-Order Logic
14249 Boolos reinterprets second-order logic as plural logic [Boolos, by Oliver/Smiley]
10830 Second-order logic metatheory is set-theoretic, and second-order validity has set-theoretic problems [Boolos]
5. Theory of Logic / C. Ontology of Logic / 1. Ontology of Logic
10829 A sentence can't be a truth of logic if it asserts the existence of certain sets [Boolos]
5. Theory of Logic / G. Quantification / 2. Domain of Quantification
10832 '∀x x=x' only means 'everything is identical to itself' if the range of 'everything' is fixed [Boolos]
5. Theory of Logic / K. Features of Logics / 4. Completeness
10834 Weak completeness: if it is valid, it is provable. Strong: it is provable from a set of sentences [Boolos]
5. Theory of Logic / K. Features of Logics / 6. Compactness
13841 Why should compactness be definitive of logic? [Boolos, by Hacking]
6. Mathematics / B. Foundations for Mathematics / 4. Axioms for Number / e. Peano arithmetic 2nd-order
10833 Many concepts can only be expressed by second-order logic [Boolos]
10. Modality / C. Sources of Modality / 5. Modality from Actuality
12468 A state of affairs is only possible if there has been an actual substance to initiate it [Pruss]
26. Natural Theory / D. Laws of Nature / 8. Scientific Essentialism / c. Essence and laws
19403 Each of the infinite possible worlds has its own laws, and the individuals contain those laws [Leibniz]