Irrelevant Conclusion

Steven Barbone

You cannot convict my client of murder. We have proven that one of the arresting officers made prejudicial remarks, remarks scornful of my client. Look at the videotape, the audiotape, the man’s own testimony.

Loosely based on the O.J. Simpson case, from PhilosophicalSociety.com

The fallacy of irrelevant conclusion, also known as the ignoratio elenchi (“igno­rance of the proof”) fallacy, is, in effect, the parent of all other fallacies since every fallacy yields a conclusion that even if it be true is not related - that is, is irrele­vant - to the premises of the argument (see also Chapter 43 on the red herring fallacy). Arguments that commit the irrelevant conclusion fallacy all end with a conclusion that is not related in any necessary way to the premises. Consider these generalizations (assume for the sake of argument that they’re true):

The Japanese eat little fat and have fewer heart attacks than Americans and the English.

The French eat a lot of fat and have fewer heart attacks than Americans and the English.

The Italians drink a lot of wine and have fewer heart attacks than Americans and the English.

The Chinese drink little wine and have fewer heart attacks than Americans and the English.

What should we conclude? How about, therefore, eat and drink as you like; speaking English leads to heart attacks! We could for the sake of argument even agree that there is some odd causal connection between speaking English and having a heart attack (so the conclusion could be correct), but does this conclusion really follow from the premises? No, it does not. In fact, it’s not certain what follows from those premises. Here’s another example of an argument with an irrelevant conclusion:

(1) The United States had an active space program in the 1960s.

(2) The USSR had an active space program in the 1960s.

(3) Therefore, the United States was the first to land humans on the moon, in 1969.

In this example, all the premises are true. The conclusion is true too, but it does not necessarily follow from the premises. Except for some who believe that the moon landing is an elaborate hoax, we should believe that humans landed on the moon in 1969, but there being active space programs does not necessarily imply that there was a moon landing.

This parent of all fallacies has no single form except that whatever the conclusion, it does not follow from the premises. We might imagine it like this:

Premise 1 + premise 2 + premise 3 [...] premise infinity.

Conclusion A (where A has nothing to do with any numerical premise).

Avoiding this fallacy is easier said than done, for it requires one to be a critical thinker at all times. Any time someone tries to persuade you of something or you try to convince someone else of something, ask how the conclusion is related to the premises. Is there a necessary, logical connection or is there merely an emotional one? Do the premises really support the conclusion or are the premises ambiguous or possibly misunderstood? Bottom line: Don’t just accept a conclusion because it’s labeled as such. Make sure it’s connected to the propositions that supposedly support it.