Ideas from 'Intro to 'Philosophy of Logic'' by Dale Jacquette [2002], by Theme Structure
[found in 'Philosophy of Logic: an anthology' (ed/tr Jacquette,Dale) [Blackwell 2002,0631218688]].
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4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / a. Systems of modal logic
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Modal logic is multiple systems, shown in the variety of accessibility relations between worlds

5. Theory of Logic / A. Overview of Logic / 1. Overview of Logic
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The two main views in philosophy of logic are extensionalism and intensionalism

5. Theory of Logic / I. Semantics of Logic / 5. Extensionalism
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Extensionalists say that quantifiers presuppose the existence of their objects

5. Theory of Logic / I. Semantics of Logic / 6. Intensionalism
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Intensionalists say meaning is determined by the possession of properties

19. Language / C. Assigning Meanings / 7. Extensional Semantics
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Extensionalist semantics forbids reference to nonexistent objects

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Extensionalist semantics is circular, as we must know the extension before assessing 'Fa'
