Combining Texts

All the ideas for 'Human Knowledge: its scope and limits', 'Morality and Art' and 'Introduction to Mathematical Logic'

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29 ideas

4. Formal Logic / B. Propositional Logic PL / 1. Propositional Logic
17749 Post proved the consistency of propositional logic in 1921 [Walicki]
17765 Propositional language can only relate statements as the same or as different [Walicki]
4. Formal Logic / B. Propositional Logic PL / 3. Truth Tables
17764 Boolean connectives are interpreted as functions on the set {1,0} [Walicki]
4. Formal Logic / F. Set Theory ST / 3. Types of Set / b. Empty (Null) Set
17752 The empty set is useful for defining sets by properties, when the members are not yet known [Walicki]
17753 The empty set avoids having to take special precautions in case members vanish [Walicki]
4. Formal Logic / F. Set Theory ST / 6. Ordering in Sets
17759 Ordinals play the central role in set theory, providing the model of well-ordering [Walicki]
5. Theory of Logic / A. Overview of Logic / 1. Overview of Logic
17741 To determine the patterns in logic, one must identify its 'building blocks' [Walicki]
5. Theory of Logic / E. Structures of Logic / 2. Logical Connectives / c. not
16489 Is it possible to state every possible truth about the whole course of nature without using 'not'? [Russell]
5. Theory of Logic / J. Model Theory in Logic / 1. Logical Models
17747 A 'model' of a theory specifies interpreting a language in a domain to make all theorems true [Walicki]
5. Theory of Logic / J. Model Theory in Logic / 3. Löwenheim-Skolem Theorems
17748 The L-S Theorem says no theory (even of reals) says more than a natural number theory [Walicki]
5. Theory of Logic / K. Features of Logics / 1. Axiomatisation
17761 A compact axiomatisation makes it possible to understand a field as a whole [Walicki]
17763 Axiomatic systems are purely syntactic, and do not presuppose any interpretation [Walicki]
6. Mathematics / A. Nature of Mathematics / 3. Nature of Numbers / e. Ordinal numbers
17758 Ordinals are transitive sets of transitive sets; or transitive sets totally ordered by inclusion [Walicki]
17755 Ordinals are the empty set, union with the singleton, and any arbitrary union of ordinals [Walicki]
17756 The union of finite ordinals is the first 'limit ordinal'; 2ω is the second... [Walicki]
17760 Two infinite ordinals can represent a single infinite cardinal [Walicki]
17757 Members of ordinals are ordinals, and also subsets of ordinals [Walicki]
6. Mathematics / B. Foundations for Mathematics / 3. Axioms for Geometry
17762 In non-Euclidean geometry, all Euclidean theorems are valid that avoid the fifth postulate [Walicki]
6. Mathematics / B. Foundations for Mathematics / 4. Axioms for Number / f. Mathematical induction
17754 Inductive proof depends on the choice of the ordering [Walicki]
10. Modality / A. Necessity / 2. Nature of Necessity
17742 Scotus based modality on semantic consistency, instead of on what the future could allow [Walicki]
10. Modality / A. Necessity / 6. Logical Necessity
16490 Some facts about experience feel like logical necessities [Russell]
12. Knowledge Sources / D. Empiricism / 5. Empiricism Critique
16488 It is hard to explain how a sentence like 'it is not raining' can be found true by observation [Russell]
19. Language / F. Communication / 3. Denial
16491 If we define 'this is not blue' as disbelief in 'this is blue', we eliminate 'not' as an ingredient of facts [Russell]
22. Metaethics / A. Ethics Foundations / 1. Nature of Ethics / b. Defining ethics
22445 Morality shows murder is wrong, but not what counts as a murder [Foot]
22. Metaethics / A. Ethics Foundations / 1. Nature of Ethics / c. Purpose of ethics
22444 A moral system must deal with the dangers and benefits of life [Foot]
22. Metaethics / B. Value / 1. Nature of Value / c. Objective value
22447 Saying something 'just is' right or wrong creates an illusion of fact and objectivity [Foot]
23. Ethics / D. Deontological Ethics / 6. Motivation for Duty
22448 We sometimes just use the word 'should' to impose a rule of conduct on someone [Foot]
25. Social Practice / F. Life Issues / 3. Abortion
22446 In the case of something lacking independence, calling it a human being is a matter of choice [Foot]
27. Natural Reality / A. Classical Physics / 1. Mechanics / a. Explaining movement
4786 Russell's 'at-at' theory says motion is to be at the intervening points at the intervening instants [Russell, by Psillos]