So what's wrong with my argument? (II)

 © 2011 by Jensen DG. Mañebog

INFORMAL FALLACIES > Fallacies of Presumption

FALLACIES OF PRESUMPTION are ineffective in providing sufficing reason for their conclusion to be accepted as true. However, in cases such as these, the erroneous reasoning is the result of an inferred supposition of some further proposition, the truth of which is doubtful or still debatable.


The fallacy of accident states some principle that is generally true and errs when it applies this principle to an accidental or exceptional case. In other words, this fallacy is committed when one takes a general rule and applies it to its atypical or exceptional cases.

            Col. de Guzman is a criminal. He killed enemies during the war and as we all know, he who kills another commits a crime.

Though it is a general rule that killing is a crime, for a soldier to do so during wars is sanctioned by the law and is therefore an exception to this general rule.

Converse Accident

It is also called “hasty generalization.” It is concluding based on insufficient or unrepresentative evidence.

Mark Caguioa has tattoo and is an excellent basketball player.

Therefore, people who have tattoo are excellent basketball players.

Notice that a single or few instances are not enough to found the truth of such a general statement. The argument is invalid since it is easy for the conclusion to be false even though the premise is true.

False Cause (post hoc ergo propter hoc)         

There was an eclipse on Monday evening.

On Tuesday morning I got migraine.

Therefore, the eclipse caused my migraine.

When one assumes that just because one event follows another then the first is the cause of the second, he commits the fallacy of false cause. It is also known aspost hoc, ergo propter hoc, meaning “after this, therefore because of this. “

Begging the Question (petitio principii)

This fallacy takes two forms:

  1. Assumptio non probata

This is committed when what has yet to be proven true is assumed as already proven true and is used as a premise for what one wants to conclude.

            All Kapampangan are boastful. (to be proven true yet) Therefore, Don, a Kapampangan, is boastful.

  1. Circular Reasoning (Circulus in probando)

 This occurs when one uses a premise to prove the conclusion and then uses the same conclusion to prove the premise.

            Jay-jay is the 1st honor of the class because he is the most intelligent of all. Why is he the most intelligent? Because he is the 1st honor of the class.

Complex Question

This fallacy assumes the truth of its own conclusion by loading it implicitly in the question that is asked:

  • Have you stopped taking prohibited drugs?

  • If so, then you admit that you do take prohibited drugs.

  • If not, then you must still be taking prohibited drugs.

  • Therefore, you are taking prohibited drugs.

Neglected Aspect

This happens when one concludes based on some evidences while “neglecting” or ignoring evidences that would endorse other conclusion.

Ex: Brand A car costs less to purchase and operate.

            (But it costs more to maintain and repair than other brands)

Brand A car therefore is the best brand.
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1. Give an original example for each of the informal fallacies discussed.

How to cite this article:
Jensen DG. Mañebog. “So what’s wrong with my argument? (II)” @
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