Post hoc

is an informal fallacy which one commits when one reasons, "Since event Y followed event X, event Y must have been caused by event X." It is a fallacy in which an event is presumed to have been caused by a closely preceding event merely on the grounds of temporal succession. This type of reasoning is fallacious because mere temporal succession does not establish a causal connection.

Examples:

• The man pulled out a gun. A shot was fired. Therefore the man fired the shot.
• You used the telephone and then it stopped working. You broke the phone.

Just because something follows something else, this is not sufficient evidence to prove true cause and effect. This temporal relationship may simply be coincidence.

Post hoc is a particularly tempting error because correlation sometimes appears to suggest causality. The fallacy lies in a conclusion based solely on the order of events, rather than taking into account other factors potentially responsible for the result that might rule out the connection.

Post hoc ergo propter hoc is an easy fallacy to detect when it is blatant, but even the best of scientists and statesmen are occasionally misled by it.