Introduction
Post Hoc Ergo Propter Hoc is the latin phrase for "after this, therefore because of this". Unlike the other fallacies already presented, this fallacy is not an "internal error", but rather it is concerned with causality. This fallacy has this structure: "A occurred before B. Therefore A caused B to happen." This fallacy is the foundation of most supersitions. Something bad happens before an event. The event turns out badly. The person blames the occurence before the event as the cause of misfortune. This argument is more difficult to disprove than most fallacies since the reason given for the event could always be true!
Definition
The fallacy which uses the existence of a preceding event as the cause of a current or future event.
Illustration
The Second Vatican Council was a disaster. Look it all of the bad things that have happened since its documents were released. Statistics don't lie. We should revoke all the documents and go back to the good old days.
Diagnosis
Post Hoc Ergo Propter Hoc is one of the most difficult fallacies to pin down because, in many cases, it is a matter of opinion whether A caused B or not. In very controversial or difficult questions of history, for instance, this fallacy is almost an inevitability. However, the more reasons one has for supporting that "A caused B", the less one can be accused of falling into this fallacy.
Antidote
The most effective way of combatting this fallacy is to do the necessary research. The supporter of the proposition has already establised that A occurred before B. Although the onus is still on him to prove the causality between the two, if his suggestion is credible, he has won a small advantage in his argument. Your job is to smash that credibility before it gets a foothold in the door. That can only be accomplished through research into the question.
John Pacheco
The Catholic Legate
February 23, 2003