Combining Texts

All the ideas for 'Relations', 'Higher-Order Logic' and 'Zettel'

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18 ideas

1. Philosophy / D. Nature of Philosophy / 1. Philosophy
2626 A philosopher is outside any community of ideas [Wittgenstein]
4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / j. Axiom of Choice IX
10301 The axiom of choice is controversial, but it could be replaced [Shapiro]
5. Theory of Logic / A. Overview of Logic / 5. First-Order Logic
10588 First-order logic is Complete, and Compact, with the Löwenheim-Skolem Theorems [Shapiro]
5. Theory of Logic / A. Overview of Logic / 7. Second-Order Logic
10298 Some say that second-order logic is mathematics, not logic [Shapiro]
10299 If the aim of logic is to codify inferences, second-order logic is useless [Shapiro]
5. Theory of Logic / B. Logical Consequence / 1. Logical Consequence
10300 Logical consequence can be defined in terms of the logical terminology [Shapiro]
5. Theory of Logic / G. Quantification / 5. Second-Order Quantification
10290 Second-order variables also range over properties, sets, relations or functions [Shapiro]
5. Theory of Logic / J. Model Theory in Logic / 3. Löwenheim-Skolem Theorems
10590 Up Löwenheim-Skolem: if natural numbers satisfy wffs, then an infinite domain satisfies them [Shapiro]
10296 The Löwenheim-Skolem Theorems fail for second-order languages with standard semantics [Shapiro]
10297 The Löwenheim-Skolem theorem seems to be a defect of first-order logic [Shapiro]
10292 Downward Löwenheim-Skolem: if there's an infinite model, there is a countable model [Shapiro]
5. Theory of Logic / L. Paradox / 6. Paradoxes in Language / a. The Liar paradox
6569 'This sentence is false' sends us in a looping search for its proposition [Wittgenstein, by Fogelin]
6. Mathematics / B. Foundations for Mathematics / 4. Axioms for Number / e. Peano arithmetic 2nd-order
10294 Second-order logic has the expressive power for mathematics, but an unworkable model theory [Shapiro]
8. Modes of Existence / A. Relations / 1. Nature of Relations
21354 It may be that internal relations like proportion exist, because we directly perceive it [MacBride]
8. Modes of Existence / A. Relations / 2. Internal Relations
21353 Internal relations are fixed by existences, or characters, or supervenience on characters [MacBride]
8. Modes of Existence / A. Relations / 4. Formal Relations / a. Types of relation
21352 'Multigrade' relations are those lacking a fixed number of relata [MacBride]
8. Modes of Existence / B. Properties / 11. Properties as Sets
10591 Logicians use 'property' and 'set' interchangeably, with little hanging on it [Shapiro]
13. Knowledge Criteria / C. External Justification / 2. Causal Justification
3790 Causes of beliefs are irrelevant to their contents [Wittgenstein]