Practice question · Sort into groups
Sort each sentence by its semantic status.
Groups: Tautology · Contradiction · Contingency
- P or not-P
- if P then P
- P and not-P
- P and Q
- if P then Q
Hints
- Check whether the sentence can be false, and whether it can be true.
- A conditional between two different atoms can go either way.
Show the answer
Tautology: if P then P, P or not-P
Contradiction: P and not-P
Contingency: P and Q, if P then Q
Why
The classification is exhaustive: a sentence is true always, never, or sometimes. Note that the conditional is contingent, not a tautology, only a conditional whose consequent is guaranteed by its antecedent is a logical truth.
Practise Tautology, Entailment and Consistency
The app has 5 more questions on this lesson, and keeps your place in the course. Philosophy I is free to start.
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