Practice question · Numerical answer
A proof of "if P then Q" by conditional introduction requires how many assumptions to be made and then discharged?
Hints
- Conditional introduction supposes the antecedent.
- That is one assumption, discharged when the conditional is concluded.
Show the answer
1
Why
One: the antecedent is assumed, the consequent derived, and the assumption discharged as the conditional is asserted. The proof that results depends only on the original premises.
Practise Natural Deduction: The Rules
The app has 3 more questions on this lesson, and keeps your place in the course. Philosophy I is free to start.
More questions on Natural Deduction: The Rules
- Arrange the steps of a conditional introduction proof in order.
- Why may a line from a closed subproof not be used later in the proof?
- Which statements about natural deduction are correct?
- Truth tables establish validity by surveying every valuation, whereas natural deduction constructs a…
- Natural deduction is strictly weaker than truth tables: some valid arguments cannot be proved in it.
- Match each proof technique to the shape of reasoning it formalises.
- Sort each rule by whether it introduces or eliminates a connective.