Proving X, Concluding Y

Description:

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

1. Evidence for claim X is presented.
2. Conclusion: Y

While all fallacies are such that the alleged evidence provided in the premise(s) fails to adequately support the conclusion, what distinguishes this fallacy is that the evidence presented actually does provide support for a claim. However, it does not support the conclusion that is actually presented.

This fallacy typically occurs when the evidence for X seems connected or relevant to Y in a logical way, but actually is not. It is this seeming relevance or connection that lures the victim into accepting the conclusion. As such, this differs from fallacies in which the victim is lured to the conclusion by an emotional appeal.

Obviously, this fallacy (like all fallacies) 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.

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!”