Reasoning: Valid Inference, Ordering, and Constraints
What this domain tests
Reasoning questions test deductive inference, ordering, constraint satisfaction, and recognition of unsupported assumptions. Fire-service scenarios may involve response sequence, equipment placement, rule compliance, or route logic. The correct answer must follow from the stated rules, not from what is plausible in real life.
Conditionals and quantifiers
- If P then Q supports two valid moves: P therefore Q, and not Q therefore not P.
- It does not support Q therefore P, or not P therefore not Q.
- All A are B means A implies B; it does not mean B implies A.
- Only A are B means B implies A.
- Unless means if not: 'unless trained, do not enter' means 'if not trained, do not enter.'
- Some means at least one; it does not mean all.
Ordering and constraints
Write slots for positions or steps, then place fixed items first. Track before, after, and adjacent as separate relationships. Use elimination: test each answer choice against every constraint and discard the first violation.
Worked example
Rule: If the bay doors are open, the exhaust fan is on. You are told the exhaust fan is on. What follows about the bay doors?
Reasoning: the rule is doors imply fan. Being told the fan is on affirms the consequent; it does not establish the doors. The fan could be on for testing. Answer: cannot be determined. If instead you were told the fan is off, the valid contrapositive gives: doors are not open.
Traps that cost marks
- Reversing a conditional.
- Treating some as all or all as some.
- Overlooking not both, at least, and except.
- Choosing a real-world truth that the premises do not support.
- Stopping after one constraint instead of checking all.