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5. Theory of Logic / B. Logical Consequence / 6. Entailment

[if P is true then Q has to be true]

2 ideas

6877	Entailment is logical requirement; it may be not(p and not-q), but that has problems [Mautner]
	Full Idea: Entailment is the modern word saying that p logically follows from q. Its simplest definition is that you cannot have both p and not-q, but this has the problem that if p is impossible it will entail every possible proposition, which seems unacceptable.
	From: Thomas Mautner (Penguin Dictionary of Philosophy [1996], p.169)
	A reaction: The word 'entail' was introduced by G.E. Moore in 1920, in preference to 'imply'. It seems clear that we need terms for (say) active implication (q must be true if p is true) and passive implication (p must be false if q is false).

14471	Analytical entailments arise from combinations of meanings and inference rules [Thomasson]
	Full Idea: 'Analytically entail' means entail in virtue of the meanings of the expressions involved and rules of inference. So 'Jones bought a house' analytically entails 'Jones bought a building'.
	From: Amie L. Thomasson (Ordinary Objects [2007], 01.2)
	A reaction: Quine wouldn't like this, but it sounds OK to me. Thomasson uses this as a key tool in her claim that common sense objects must exist.