Thursday, December 6, 2007

a logical fallacy: Post hoc, ergo propter hoc

Recent headlines regarding the increase in teen pregnancy rates (e.g., U.S. teen pregnancy rate rises) have provoked more than a few folks to condemn W's funding of "abstinence only" sex-education programs.

Now, I think "abstinence only" programs are pretty silly, and there's some legitimate research available that suggests they're not effective,...
BUT... the observation that teen pregnancy rates have increased after W funded "abstinence only" programs does NOT imply that W's funding of "abstinence only" programs caused the increase in teen pregnancy rates.

This reasoning is an example of a classical logical fallacy:
Post hoc, ergo propter hoc
... which is Latin (this really is a classical fallacy!) for
"After this, therefore because of this."

The Wikipedia entry is pretty good:
"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. Most familiarly, many superstitious beliefs and magical thinking arise from this fallacy."

Note: W's funding of "abstinence only" programs may, in fact, be the cause of the recent increase in teen pregnancy. BUT the arguments advanced to date are not logically compelling! If the case can be made, make it!... but don't rely on intellectually lazy and dishonest argumentation!

Regarding the relationship to "magical thinking", one recent example (from yesterday!) is Senator Clinton's observation that the Kyl-Lieberman Amendment caused Iran to reduce its influence in Iraq!

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