Combining Philosophers

All the ideas for Pherecydes, Augustus De Morgan and Gerhard Gentzen

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11 ideas

5. Theory of Logic / A. Overview of Logic / 2. History of Logic
11022 Gentzen introduced a natural deduction calculus (NK) in 1934 [Gentzen, by Read]
5. Theory of Logic / E. Structures of Logic / 2. Logical Connectives / a. Logical connectives
11065 The inferential role of a logical constant constitutes its meaning [Gentzen, by Hanna]
11023 The logical connectives are 'defined' by their introduction rules [Gentzen]
11213 Each logical symbol has an 'introduction' rule to define it, and hence an 'elimination' rule [Gentzen]
5. Theory of Logic / E. Structures of Logic / 6. Relations in Logic
13501 De Morgan found inferences involving relations, which eluded Aristotle's syllogistic [De Morgan, by Hart,WD]
17744 De Morgan started the study of relations and their properties [De Morgan, by Walicki]
5. Theory of Logic / G. Quantification / 2. Domain of Quantification
17743 De Morgan introduced a 'universe of discourse', to replace Boole's universe of 'all things' [De Morgan, by Walicki]
5. Theory of Logic / H. Proof Systems / 4. Natural Deduction
13832 Natural deduction shows the heart of reasoning (and sequent calculus is just a tool) [Gentzen, by Hacking]
6. Mathematics / B. Foundations for Mathematics / 4. Axioms for Number / g. Incompleteness of Arithmetic
10067 Gentzen proved the consistency of arithmetic from assumptions beyond arithmetic [Gentzen, by Musgrave]
26. Natural Theory / A. Speculations on Nature / 6. Early Matter Theories / c. Ultimate substances
22745 Pherecydes said the first principle and element is earth [Pherecydes, by Sext.Empiricus]
29. Religion / D. Religious Issues / 2. Immortality / a. Immortality
5883 Pherecydes was the first to say that the soul is eternal [Pherecydes, by Cicero]