WordNet
n. the logical fallacy of believing that temporal succession implies a causal relation [syn: post hoc]
Wikipedia
Post hoc ergo propter hoc ( Latin: "after this, therefore because of this") is a logical fallacy (of the questionable cause variety) that states "Since event Y followed event X, event Y must have been caused by event X." It is often shortened to simply post hoc fallacy. It is subtly different from the fallacy cum hoc ergo propter hoc ("with this, therefore because of this"), in which two things or events occur simultaneously or the chronological ordering is insignificant or unknown. Post hoc is a particularly tempting error because temporal sequence appears to be integral to causality. The fallacy lies in coming to a conclusion based solely on the order of events, rather than taking into account other factors that might rule out the connection.
The following is a simple example:
Usage examples of "post hoc ergo propter hoc".
Perhaps it was only post hoc ergo propter hoc, but at any rate, he made no further attempt to prevent me and my friend from ascending the byway.