Combining Texts

All the ideas for 'The Sign of Four', 'English as a Formal Language' and 'Set Theory and related topics (2nd ed)'

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3 ideas

4. Formal Logic / F. Set Theory ST / 3. Types of Set / e. Equivalence classes
Equivalence relations are reflexive, symmetric and transitive, and classify similar objects [Lipschutz]
     Full Idea: A relation R on a non-empty set S is an equivalence relation if it is reflexive (for each member a, aRa), symmetric (if aRb, then bRa), and transitive (aRb and bRc, so aRc). It tries to classify objects that are in some way 'alike'.
     From: Seymour Lipschutz (Set Theory and related topics (2nd ed) [1998], 3.9)
     A reaction: So this is an attempt to formalise the common sense notion of seeing that two things have something in common. Presumably a 'way' of being alike is going to be a property or a part
5. Theory of Logic / F. Referring in Logic / 2. Descriptions / b. Definite descriptions
'The' is a quantifier, like 'every' and 'a', and does not result in denotation [Montague]
     Full Idea: The expression 'The' turns out to play the role of a quantifier, in complete analogy with 'every' and 'a', and does not generate (in common with common noun phrases) denoting expressions
     From: Richard Montague (English as a Formal Language [1970], p.216), quoted by Bernard Linsky - Quantification and Descriptions 4
     A reaction: Linsky says that it is now standard to interpret definite descriptions as quantifiers
14. Science / C. Induction / 1. Induction
If you eliminate the impossible, the truth will remain, even if it is weird [Conan Doyle]
     Full Idea: When you have eliminated the impossible, whatever remains, however improbable, must be the truth.
     From: Arthur Conan Doyle (The Sign of Four [1890], Ch. 6)
     A reaction: A beautiful statement, by Sherlock Holmes, of Eliminative Induction. It is obviously not true, of course. Many options may still face you after you have eliminated what is actually impossible.