Non sequitur

Non sequitur ( Latin for “it does not follow”) is a fallacy within the argumentation of a proof that is based on the fact that the inferred thesis cannot be derived from the underlying premises . It is a non sequitur if, in the attempted proof of the thesis, arguments are put forward that are true but do not offer a sufficient reason for the truth of the thesis.

Examples:

	The universe had a beginning.

'non sequitur'	So it also has an end.

Both statements can be correct, but this is neither certain, nor is the existence of a beginning sufficient to necessarily require an end. There is no rule "Everything that has a beginning has an end" that can be disputed regardless of the conclusion or premise. If this missing premise is shared by the audience, then it can be an enthymeme .

	When I'm in Vienna, I'm in Austria.
	I am not in Vienna.
'non sequitur'	That's why I'm not in Austria.

Even if both premises apply, the conclusion does not have to be correct, because I could be in another place in Austria (outside of Vienna). This example is an incorrectly applied contraposition : “From statement A follows statement B ” does not mean, conversely, “from not A does not follow B ”. Correct is: “Not B does not follow A”, so analogous to the above example would be correct: “I'm not in Austria, so I'm not in Vienna either”.