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Single Idea 14532

[filed under theme 10. Modality / A. Necessity / 3. Types of Necessity ]

Full Idea

Rumfitt argues that there is a distinctive notion of necessity implicated in the notion of logical consequence.

Gist of Idea

A distinctive type of necessity is found in logical consequence

Source

report of Ian Rumfitt (Logical Necessity [2010]) by Bob Hale/ Aviv Hoffmann - Introduction to 'Modality' 2

Book Ref

'Modality', ed/tr. Hale,B/Hoffman,A [OUP 2010], p.10


The 11 ideas from 'Logical Necessity'

A distinctive type of necessity is found in logical consequence [Rumfitt, by Hale/Hoffmann,A]
Logical necessity is when 'necessarily A' implies 'not-A is contradictory' [Rumfitt]
Contradictions include 'This is red and not coloured', as well as the formal 'B and not-B' [Rumfitt]
Soundness in argument varies with context, and may be achieved very informally indeed [Rumfitt]
Geometrical axioms in logic are nowadays replaced by inference rules (which imply the logical truths) [Rumfitt]
There is a modal element in consequence, in assessing reasoning from suppositions [Rumfitt]
We reject deductions by bad consequence, so logical consequence can't be deduction [Rumfitt]
A logically necessary statement need not be a priori, as it could be unknowable [Rumfitt]
Narrow non-modal logical necessity may be metaphysical, but real logical necessity is not [Rumfitt]
If a world is a fully determinate way things could have been, can anyone consider such a thing? [Rumfitt]
The logic of metaphysical necessity is S5 [Rumfitt]