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### Single Idea 21612

#### [catalogued under 5. Theory of Logic / H. Proof Systems / 4. Natural Deduction]

Full Idea

Argument by Cases (or or-elimination) is the standard way of using disjunctive premises. If one can argue from A and some premises to C, and from B and some premises to C, one can argue from 'A or B' and the combined premises to C.

Gist of Idea

Or-elimination is 'Argument by Cases'; it shows how to derive C from 'A or B'

Source

Timothy Williamson (Vagueness [1994], 5.3)

Book Reference

Williamson,Timothy: 'Vagueness' [Routledge 1996], p.152