Logical Reasoning
Logical reasoning in NATA tests whether you can move from given information to a conclusion that must follow, and whether you can spot the rule in a sequence or analogy. It rewards precision: the conclusion must be justified by the premises, not by what seems true in the real world.
Core rules and concepts
- Deduction: in a valid argument, if the premises are true the conclusion cannot be false.
- Conditionals: “If P then Q” permits Q when P is true, and not-P when Q is false (the contrapositive). It does not permit Q therefore P, or not-P therefore not-Q.
- Quantifiers: “All A are B” does not imply “All B are A”; “some A are B” is the same as “some B are A”.
- Series: compare differences, ratios, alternating operations, squares/cubes and positions.
- Elimination: use constraints to remove impossible options rather than guessing.
Worked example
Find the next term: 3, 8, 15, 24, 35, __. The differences are 5, 7, 9, 11-consecutive odd numbers-so the next difference is 13 and the next term is 48. A second valid description is n² − 1 for n = 2, 3, 4, 5, 6; the next term is 7² − 1 = 48. Both rules agree, which strengthens confidence. If two rules disagree, test each against every given term and choose the one that explains all of them with the fewest assumptions.
Traps that cost marks
The commonest errors are affirming the consequent (“If it is a studio, it has north light; this room has north light, so it is a studio”) and denying the antecedent. Do not import outside knowledge that contradicts the premises. Do not assume a sequence is arithmetic before checking ratios or alternating patterns. In syllogisms, watch for a term that appears in both premises but is not distributed, which often makes an invalid conclusion look plausible.