In the deduction section of a critical thinking test, a conclusion follows only if it must be true whenever the statements are true. Two kinds of statement come up: statements about groups ("all", "some", "no") and if-then rules.
If-then rules have two valid moves and two traps. Take "If it rains, the match is moved indoors."
- It rained, so the match was moved indoors: follows.
- The match wasn't moved indoors, so it didn't rain: follows. If it had rained, the match would have moved.
- The match was moved indoors, so it rained: doesn't follow. It might have moved for another reason.
- It didn't rain, so the match wasn't moved: doesn't follow. The rule says nothing about dry days.
Two rules can also chain: if A then B, and if B then C, so if A then C.
Judge only the logic. A conclusion can be true in real life and still not follow, or follow from statements that are false.