Combining Texts

All the ideas for 'Academica', 'A Tour through Mathematical Logic' and 'On Freedom'

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30 ideas

2. Reason / C. Styles of Reason / 1. Dialectic
2661 Dialectic is speech cast in the form of logical argument [Cicero]
3. Truth / A. Truth Problems / 1. Truth
2673 There cannot be more than one truth [Cicero]
4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / b. Terminology of PL
13520 A 'tautology' must include connectives [Wolf,RS]
4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / c. Derivation rules of PL
13524 Deduction Theorem: T∪{P}|-Q, then T|-(P→Q), which justifies Conditional Proof [Wolf,RS]
4. Formal Logic / C. Predicate Calculus PC / 2. Tools of Predicate Calculus / d. Universal quantifier ∀
13521 Universal Specification: ∀xP(x) implies P(t). True for all? Then true for an instance [Wolf,RS]
13522 Universal Generalization: If we prove P(x) with no special assumptions, we can conclude ∀xP(x) [Wolf,RS]
4. Formal Logic / C. Predicate Calculus PC / 2. Tools of Predicate Calculus / e. Existential quantifier ∃
13523 Existential Generalization (or 'proof by example'): if we can say P(t), then we can say something is P [Wolf,RS]
4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / e. Axiom of the Empty Set IV
13529 Empty Set: ∃x∀y ¬(y∈x). The unique empty set exists [Wolf,RS]
4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / n. Axiom of Comprehension
13526 Comprehension Axiom: if a collection is clearly specified, it is a set [Wolf,RS]
5. Theory of Logic / A. Overview of Logic / 5. First-Order Logic
13534 In first-order logic syntactic and semantic consequence (|- and |=) nicely coincide [Wolf,RS]
13535 First-order logic is weakly complete (valid sentences are provable); we can't prove every sentence or its negation [Wolf,RS]
5. Theory of Logic / D. Assumptions for Logic / 2. Excluded Middle
2669 Dialectic assumes that all statements are either true or false, but self-referential paradoxes are a big problem [Cicero]
5. Theory of Logic / J. Model Theory in Logic / 1. Logical Models
13519 Model theory uses sets to show that mathematical deduction fits mathematical truth [Wolf,RS]
13531 Model theory reveals the structures of mathematics [Wolf,RS]
13532 Model theory 'structures' have a 'universe', some 'relations', some 'functions', and some 'constants' [Wolf,RS]
13533 First-order model theory rests on completeness, compactness, and the Löwenheim-Skolem-Tarski theorem [Wolf,RS]
5. Theory of Logic / J. Model Theory in Logic / 2. Isomorphisms
13537 An 'isomorphism' is a bijection that preserves all structural components [Wolf,RS]
5. Theory of Logic / J. Model Theory in Logic / 3. Löwenheim-Skolem Theorems
13539 The LST Theorem is a serious limitation of first-order logic [Wolf,RS]
5. Theory of Logic / K. Features of Logics / 4. Completeness
13538 If a theory is complete, only a more powerful language can strengthen it [Wolf,RS]
5. Theory of Logic / K. Features of Logics / 10. Monotonicity
13525 Most deductive logic (unlike ordinary reasoning) is 'monotonic' - we don't retract after new givens [Wolf,RS]
6. Mathematics / A. Nature of Mathematics / 3. Nature of Numbers / e. Ordinal numbers
13530 An ordinal is an equivalence class of well-orderings, or a transitive set whose members are transitive [Wolf,RS]
6. Mathematics / B. Foundations for Mathematics / 6. Mathematics as Set Theory / a. Mathematics is set theory
13518 Modern mathematics has unified all of its objects within set theory [Wolf,RS]
10. Modality / B. Possibility / 5. Contingency
5040 Necessary truths can be analysed into original truths; contingent truths are infinitely analysable [Leibniz]
10. Modality / D. Knowledge of Modality / 2. A Priori Contingent
13159 Only God sees contingent truths a priori [Leibniz]
10. Modality / E. Possible worlds / 3. Transworld Objects / e. Possible Objects
5039 If non-existents are possible, their existence would replace what now exists, which cannot therefore be necessary [Leibniz]
12. Knowledge Sources / B. Perception / 1. Perception
2664 If we have complete healthy senses, what more could the gods give us? [Cicero]
12. Knowledge Sources / E. Direct Knowledge / 4. Memory
2665 How can there be a memory of what is false? [Cicero]
13. Knowledge Criteria / D. Scepticism / 3. Illusion Scepticism
20800 Every true presentation can have a false one of the same quality [Cicero]
23. Ethics / C. Virtue Theory / 2. Elements of Virtue Theory / c. Motivation for virtue
2672 Virtues must be very detached, to avoid being motivated by pleasure [Cicero]
28. God / A. Divine Nature / 3. Divine Perfections
5041 God does everything in a perfect way, and never acts contrary to reason [Leibniz]