Repeating the question from the title

Question. How does one call an argument where premises do not necessarily lead to a conclusion?

By "not necessarily lead to a conclusion", I mean that given the premises are true, the conclusion may or may not be true (i.e., further justification is required). To make things concrete, let's consider following simple argument as an example:

Argument. Some prostitutes are being treated very badly. Therefore, prostitution should be banned.

The argument doesn't seem to be invalid (at least I don't see what "counterexample" one can come up with to invalidate it), but at the same time I don't see how the argument is valid. It is clear that the issue surrounding prostitution is complicated, and there is definitely some contention about whether prostitution should be legalized. And so it seems to me that "some prostitutes are being treated very badly" is simply not a sufficient evidence to justify the ban of the prostitution.

So coming back to the question: how does one call an argument where it is possible that the conclusion is true, but the premises listed are not sufficient to prove it?

  • 1
    "non sequitur" ?
    – armand
    Commented May 10, 2021 at 22:47
  • If the premises do not lead to the conclusion then the argument is invalid. Your example is particularly suspect as it concludes a "should" from an "is", which is arguably always invalid, see Is–ought problem. However, valid arguments are sometimes presented with missing steps that are expected to be filled in from context, those are called enthymemes. Your example can be interpreted as enthymeme where the audience is expected to fill in the premise.
    – Conifold
    Commented May 11, 2021 at 0:20
  • hasty generalization, is ought Commented May 11, 2021 at 19:04

2 Answers 2


The expression: "an argument where the premises do not necessarily lead to the conclusion" covers many possibilities. It could include among other things...

  • arguments that are intended to be deductive, but are flawed because of a formal defect in the logic;
  • arguments that have unstated or assumed premises that are needed to make them valid (enthymemes);
  • arguments that are not intended to be deductive, but where the premises are given to support the conclusion, perhaps because the conclusion offers the best explanation of the premises (abductive reasoning), or because the premises might be considered to provide statistical support for the conclusion (inductive reasoning);
  • arguments by analogy;
  • arguments that are based upon some agreed or assumed moral or practical principles.

To say of an argument that the premises do not necessarily lead to the conclusion does not imply that it must be a bad argument, so it is not appropriate to label it a fallacy. Probably the most general term that describes what you want is simply "not deductively valid".


You could call it incoherent, invalid, unsound. This does not mean your conclusion is false just that your argument is not acceptable.

If you replace "prostitutes/prostitution" with "cleaners/working as a cleaner" your argument just falls apart.

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