Proving X, Concluding Y




Also Known As:  Missing the Point, Irrelevant Thesis


This fallacy occurs when a conclusion is drawn from evidence that does not support that conclusion but does support another claim.  The form of this reasoning is as follows:


Premise 1: Evidence E for claim X is presented.

Conclusion: Therefore, Y


While all fallacies of reasoning are cases where the evidence fails to adequately support the conclusion, what distinguishes this fallacy is that the evidence presented does provide support for a claim. However, it does not support the conclusion presented.

This fallacy typically occurs when the evidence for X appears vaguely connected or relevant to Y in a logical way but is not. It is this seeming relevance or connection that provides the psychological force for the fallacy. This fallacy can be inflicted on others or oneself and committed in good or bad faith. When committed in good faith, the person is ignorant of the fallacy. When committed in bad faith, the fallacy is intentionally committed.

When a person uses this fallacy in bad faith, they exploit the apparent logical connection between the evidence and the conclusion to mislead someone into accepting the reasoning. This could, perhaps, be called “the bait and switch fallacy.” For example, a politician might advance evidence that a problem exists, then use that evidence to “prove” that some other vaguely similar problem exists.

Obviously, this fallacy (like all fallacies of reasoning) is a case of non-sequiter (“does not follow”) in which the conclusion does not logically follow from the premises. However, this specific sort of mistake is common and interesting enough to justify giving it its own name and entry.


Defense: The defense against this fallacy is also a good general defense against bad reasoning: before accepting a conclusion, carefully consider whether the evidence provided supports that conclusion.


Example #1

“I am troubled by the reports of binge drinking by college students. According to the statistics I have seen, about 19% of college students are binge drinkers and this leads to problems ranging from poor academic performance to unplanned pregnancies. Since people often drink in response to pressure, this shows that professors are putting their students under too much pressure and hence need to make their classes easier.”


Example #2

“Our product testing revealed that 60% of the people on Acme Diet Master reported that they felt less hungry when using the product.  This shows that 60% ate less when using our product. I think we have our next big product!”


Example #3

“High tax rates for individuals leave them with far less money to spend. High tax rates for business often leads them to lower salaries, which means people have far less money to spend. In these troubled economic times, revitalizing the economy requires that Americans spend more. Therefore, the obvious solution is to abolish all taxes.”

Originally appeared on A Philosopher’s Blog Read More