Classically, the term non sequitur applies to:
- A conclusion that does not follow from the premises or evidence.
- A statement that does not necessarily follow from preceding statements.
The most common example of non sequitur is any attempt to infer causation from correlation alone. An argument of causality--that is, that X caused Y--is always subject to weakening if one can show that:
- Y could have occurred with or without X.
- Another event, Z, could have caused Y.
- Y caused X rather than X causing Y.
The usual way to weaken a non sequitur is simply to show that two facts, that might happen to correlate, are in fact not mutually relevant. Of course, showing that the chain of implication is reversed--meaning that the first named fact actually follows from the second, rather than the second from the first--will cast even more serious doubt on the argument.
- Glenn Whitman, Non sequitur, Glen Whitman's Debate Page, August 30, 2005. Retrieved April 9, 2007.
- Definition of non sequitur in The American Heritage® Dictionary of the English Language, 4th. ed., Houghton Mifflin Company, 2006. Retrieved April 9, 2007.
- Paul Raveling, Non sequitur logical fallacies at SierraFoot.org. Retrieved April 9, 2007.