The fallacy of questionable cause (or non causa pro causa) occurs when an arguer asserts a non-trivial causal relationship without presenting evidence of a mechanism of causality.

Other than cases of directly observable, immediate physical causation (like seeing a hammer drive in a nail), causality is difficult to know without supporting explanation. In matters that are less obvious, a flat assertion of causality that is leveraged argumentatively is fallacious, because the supposed causality is being presumed without its having been logically demonstrated.

Here is an example of the fallacy:

"Rock music should be banned in the school dining hall because it interrupts food digestion."

This would not be an easily observable, direct causation, and so should not be used to argue for the banning of rock music, without further evidence being provided about the purported causality.

Note that when we recognize an occurrence of this fallacy, it does not mean necessarily that the asserted cause doesn't exist. The occurrence of the fallacy means that drawing the conclusion that the cause exists is unwarranted by the evidence presented.

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