Recently I came across the following line of reasoning.

The reason is because it is COMMON SENSE, which many do not have.

Obviously something goes wrong here as per definition of common sense many people must obey to it/have it. In essence it is the very reverse of a tautology (in the logical sense). How should one classify this error? Is there a specific name to that classification? And with regard to rhetorics, what purpose could such a invalid construction have (such that it can be labeled a fallacy)? Or is it just an oddity of an irrational or confused mind?

  • 1
    The usual term for this is an oxymoron. It is not a fallacy. One might be used ironically, or as a device to call attention to an inconsistency.
    – Bumble
    Feb 17, 2016 at 22:45
  • @Bumble Oh yes, that was the term. But, I should add that this was stated in a serious context (at least from the speaker's point of view).
    – Jori
    Feb 17, 2016 at 22:48
  • 2
    Oxymorons may not be fallacies even when used seriously, there is a difference between etymology of a phrase and its colloquial meaning. Modern dictionaries often treat "common sense" as an idiom, it is not literally a sense, nor does it have to be common. Merriam-Webster describes it as "sound and prudent judgment based on a simple perception of the situation or facts". On this description it is possible that nobody has it.
    – Conifold
    Feb 18, 2016 at 2:38
  • Another example is, "It's wrong to subject a Social science like History to the Scientific method." Statements like this are used rhetorically to win arguments, however cheaply.
    – Cormagh
    Aug 9, 2017 at 0:56

2 Answers 2


I'd be tempted to call it an is-ought failure, although it is presented in the inverse of the usual relationship.* Typically when a speaker is using this construction, they believe the reason ought to be common sense, but they choose to claim that the reason is common sense instead.

This often occurs in situations where the speaker really doesn't want to take the time to get into the reason, or perhaps doesn't even have enough of a introspective understanding of the reason to subject it to questioning.

* Most sources I see consider the is-ought problem to be when people take what "is" and assume it is what "ought" to be. In this case, you likely have someone who is taking what they believe it "ought" to be, and calling it "is"


What an interesting question! A tautology is always true. P always implies P. So what to say of a statement that is internally contradictory, at least partially, and thus often untrue? "My argument is based on common sense, which is often uncommon."

I end up agreeing with Cort Ammon that the issue is an is-ought problem. The speaker is really saying that all people should have common sense. "All people" includes the puzzled listener. The claim is also a sort of ad hominem argument, as it contains the implication that there is something wrong with the listener's ability to reason.

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