Ideas of C.I. Lewis, by Theme
[American, 1883  1964, Born at Stoneham. Professor at Harvard University.]
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4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / h. System S5
7791

The simplest of the logics based on possible worlds is Lewis's S5 [Girle]

5. Theory of Logic / A. Overview of Logic / 1. Overview of Logic
9358

There are several logics, none of which will ever derive falsehoods from truth

5. Theory of Logic / D. Assumptions for Logic / 2. Excluded Middle
9357

Excluded middle is just our preference for a simplified dichotomy in experience

5. Theory of Logic / F. Referring in Logic / 1. Naming / a. Names
9364

Names represent a uniformity in experience, or they name nothing

10. Modality / A. Necessity / 2. Nature of Necessity
11002

Equating necessity with informal provability is the S4 conception of necessity [Read]

10. Modality / A. Necessity / 11. Denial of Necessity
9362

Necessary truths are those we will maintain no matter what

10. Modality / B. Possibility / 8. Conditionals / a. Conditionals
7803

Modal logic began with translation difficulties for 'If...then' [Girle]

12. Knowledge Sources / A. A Priori Knowledge / 7. A Priori from Convention
9365

We can maintain a priori principles come what may, but we can also change them

13. Knowledge Criteria / B. Internal Justification / 4. Foundationalism / a. Foundationalism
6556

If anything is to be probable, then something must be certain

18. Thought / C. Content / 8. Intension
5828

Extension is the class of things, intension is the correct definition of the thing, and intension determines extension

18. Thought / E. Abstraction / 2. Abstracta by Selection
9361

We have to separate the mathematical from physical phenomena by abstraction

26. Natural Theory / D. Laws of Nature / 8. Scientific Essentialism / a. Scientific essentialism
9363

Science seeks classification which will discover laws, essences, and predictions
