Combining Philosophers

Ideas for Hermarchus, Theodore Sider and Gottfried Leibniz

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4 ideas

5. Theory of Logic / K. Features of Logics / 1. Axiomatisation
It is always good to reduce the number of axioms [Leibniz]
     Full Idea: To reduce the number of axioms is always something gained.
     From: Gottfried Leibniz (New Essays on Human Understanding [1704], 4.06)
     A reaction: This is rather revealing about the nature of axioms. They don't have any huge metaphysical status - in fact one might say that their status is epistemological, or even pedagogic. They enable us to get out minds round things.
5. Theory of Logic / K. Features of Logics / 4. Completeness
In a complete logic you can avoid axiomatic proofs, by using models to show consequences [Sider]
     Full Idea: You can establish facts of the form Γ|-φ while avoiding the agonies of axiomatic proofs by reasoning directly about models to conclusions about semantic consequence, and then citing completeness.
     From: Theodore Sider (Logic for Philosophy [2010], 4.5)
     A reaction: You cite completeness by saying that anything which you have shown to be a semantic consequence must therefore be provable (in some way).
5. Theory of Logic / K. Features of Logics / 5. Incompleteness
We can assign a characteristic number to every single object [Leibniz]
     Full Idea: The true principle is that we can assign to every object its determined characteristic number.
     From: Gottfried Leibniz (Towards a Universal Characteristic [1677], p.18)
     A reaction: I add this as a predecessor of Gödel numbering. It is part of Leibniz's huge plan for a Universal Characteristic, to map reality numerically, and then calculate the truths about it. Gödel seems to allow metaphysics to be done mathematically.
5. Theory of Logic / K. Features of Logics / 6. Compactness
Compactness surprisingly says that no contradictions can emerge when the set goes infinite [Sider]
     Full Idea: Compactness is intuitively surprising, ..because one might have thought there could be some contradiction latent within some infinite set, preventing it from being satisfiable, only discovered when you consider the whole set. But this can't happen.
     From: Theodore Sider (Logic for Philosophy [2010], 4.5)