Logical Reasoning and General Aptitude: Valid Deduction
Logical Reasoning and General Aptitude tests deductive validity, conditional reasoning, pattern recognition, data interpretation, spatial judgment, and careful reading. Many items are deliberately worded so that a plausible everyday conclusion is not logically forced.
Core rules and concepts
- In a valid deduction, the conclusion must be true whenever the premises are true. Validity is about structure, not whether the premises are factually true.
- For 'All A are B', every A lies inside B. For 'No A are B', the two sets are disjoint. For 'Some A are B', at least one A is also B; it does not mean some A are not B.
- Conditional 'If P then Q' supports modus ponens (P, therefore Q) and modus tollens (not Q, therefore not P). It does not support 'Q, therefore P' or 'not P, therefore not Q'.
- In number series, check differences, ratios, alternating patterns, and squares or primes before assuming a single rule.
- In data interpretation, read the axis labels and units first; compare like with like, and distinguish a percentage from a percentage point.
- In spatial items, rotate the figure mentally and track left-right reversals; do not rely on the first orientation that looks familiar.
Worked example
Premises: All nurses are health workers. No health workers are volunteers. What follows? The first premise places every nurse inside the health-worker set. The second says the health-worker set and the volunteer set do not overlap. Therefore no nurse can be a volunteer. The conclusion 'No nurses are volunteers' is valid. By contrast, from 'All nurses are health workers' and 'Some health workers are men', you cannot conclude 'Some nurses are men': the men could be health workers who are not nurses. This distinction between what is guaranteed and what is merely possible is the core skill.
Traps
Affirming the consequent and denying the antecedent are the most common formal errors. Treating 'some' as 'some but not all' is another. In charts, a small absolute difference can look large if the axis is truncated. In attention-to-detail items, check names, dates, and negation words before choosing.