Discussion

Match List-I with List-II and give your answer using the codes given below :

List-I (Type of Reasoning)	List II (Example)
(P) Modus ponens	(1) The switch is not turned on; therefore the fan is not running.
(Q) Modus tollens	(2) The switch is turned on; therefore the fan is running
(R) Denial of the antecedent	(3) The fan is running; therefore the switch is turned on
(S) Affirmation of the consequent	(4) The fan is not running; therefore the switch is not turned on

Answer: B

The correct matching is P-2, Q-4, R-1, S-3.

Take the rule 'if the switch is turned on, the fan is running'.

P: modus ponens affirms the antecedent: the switch is on, so the fan is running (2). Valid.
Q: modus tollens denies the consequent: the fan is not running, so the switch is not on (4). Valid.
R: denial of the antecedent: the switch is not on, so the fan is not running (1). Invalid, as the fan could be running for another reason.
S: affirmation of the consequent: the fan is running, so the switch is on (3). Invalid for the same reason.

The first code swaps the two fallacies; the others misplace the valid forms as well.

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