"If the plane takes off from the airstrip B then it is south bound. The plane did not take off from the airstrip B, therefore it is not southbound." Identify the formal fallacy in the above argument.
Denying the antecedent
First put the argument in conditional form. The premise is: If (plane takes off from airstrip B) then (it is southbound). Call the "if" part the antecedent (A: takes off from B) and the "then" part the consequent (C: southbound). So the premise is A → C.
The argument then says: the plane did NOT take off from B (that is, not-A), therefore it is NOT southbound (not-C). In pattern form: A → C; not-A; therefore not-C.
This is invalid because a conditional guarantees the consequent only when the antecedent holds; it says nothing about what happens when the antecedent fails. The plane could be southbound for some other reason even without using airstrip B. Rejecting the consequent merely because the antecedent was rejected is the fallacy of Denying the antecedent.
Why not the others: Affirming the consequent is the different invalid pattern (A → C; C; therefore A) — here we deny, not affirm. Exclusive premises and fallacy of four terms are errors of categorical syllogisms, not of a single conditional argument like this one.
Similar Questions
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Important Questions from Formal and Informal Fallacies
Which logical fallacy is committed in the following statement - "I do not believe that serial killers ought to be allowed to live. They have forfeited their right to live because anyone who kills lots of people has lost that right".
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Choose the correct answer from the options given below:
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