Post hoc, propter hoc - "after the fact, therefore because of the fact"


This fallacy not only shows up in fairly common, every-day examples from popular culture, advertising, campaign rhetoric, etc. - as some of the later examples suggest, this fallacy raises serious questions in the philosophy of science concerning empirical evidence as "proof" of hypothetical causal relationships.


1. Basketball star Bill Walton of the Boston Celtics, now recovering from an ankle injury, says that adding meat to his diet turned his life and game around. The strapping 6ft.11in. hoopster was plagued by health problems as a vegetarian thoughout his career. But last year, he played 80 out of 82 games as a meat-eater - a record for him.

"Adding meat to his diet helped make him physically stronger," says Jeff Twiss, an officer of the Celtics. "The doctors convinced him he needed meat."

2. President Bush accuses Gov. Bill Clinton of being a "tax and spend" Democrat. He notes that state government spending in Arkansas had doubled since 1982, and most of that increase has been financed through regressive measures such as sales taxes.

[In considering the above, take into account the following:

What President Bush doesn't say is that state government spending in Missouri has likewise doubled in the past decade -- under Republican governors.

In fact, virtually every state's spending has doubled or increased substantially over the past decade -- because the federal government, under the Reagan and Bush presidencies, has dumped more and more responsibilities onto them without providing any additional revenue to help pay for them. (That is, as social services -- from highway funding through education to welfare programs -- were drastically cut back as part of the Reagan/Bush program, states found themselves forced to fill in the gaps left behind by a retreating federal government -- but with no additional funds from the federal government to help pay for these services.)

Indeed, Missouri -- again, under Republican leadership -- has relied on similarly regressive tax increases (on sales, gasoline, cigarettes and wine) to finance its increased spending.

So be extra careful this year as you watch those political commercials and listen to those speeches.

(From: Keith White, "Beware of politicians fictionalizing facts," The News-Leader, Sunday, September 27, 1992, 2E.)

3. There was no appreciable crime related to drugs when they were legal.

Crime rate has increased since they have been made illegal.

Therefore, drugs should be legal since legalization would improve the "quality of life" in the U.S.

4. Smoking marijuana definitely leads to heroin use. A report by the U.S. Commissioner of Narcotics on a study of 2,213 hardcore narcotic addicts in the Lexington, Kentucky, Federal Hospital shows that 70.4% smoked marijuana _before_ taking heroin.

5. We had a pile of rags in the corner.

Pretty soon we noticed rats hanging around the pile of rags.

/.. rags cause rats

6. Chrysler Corporation turned around from having to be bailed out by the United States Government (yes, Virginia, socialism is alive and well in the U.S....) to a highly profitable company - all after they brought Lee Iococa on board as their chief CEO.

/.. Iococa must be a great businessman.

7. Pornography should be illegal because studies show that most convicted sexual offenders report regular use of such materials.

Note: this example also contains fallacy of denying the antecedent.

8.  If human beings are simply complicated, clock-like mechanisms, then their behavior is fully determined by some set of causal factors. And if behavior is determined, then it is predictable.

We find, in fact, that much human behavior is predictable. Indeed, we take it as a sign of how well we know someone that we can predict their likes, dislikes, and responses to certain choices.

So human behavior must be simply the result of causal determination.

9.  A lawyer for cancer victims sueing the Three Mile Island nuclear power plant owners argued:

After the accident at Three Mile Island, cancer rates in an area defined by a 10 mile radius from the plant increased by anywhere from 50% to 100%. Some cancers, indeed, increased even more: lung cancer rates went up 400% to 700%.

Clearly, Three Mile Island is responsible for these increased cancer incidents; the plant owners should thus be held responsible for compensatory and punitive damages.

10. If my hypothesis is correct, then the cause of rabies is a rabies germ that is carried by rabid animals. If this hypothesis is correct, then if we inject a vaccine in animals that kills rabies germs, we would expect the disease to disappear.

In fact, we find that if we inject the vaccine in animals, the disease disappears. So my hypothesis must be correct.

11. The Communist Manifesto, by Karl Marx and Friedrich Engels, laid out ten interim measures for moving developed countries toward Communism. By the mid 1950's, the United States had implemented, in whole or in part, eight of the ten planks.

For example, Marx and Engels called for: (1) the abolition of property in land and application of all rents of land to public purposes; (2) centralization of credit in the hands of the state, by means of a national bank with state capital and an exclusive monopoly; (3) centralization of the means of communication and transport in the hands of the state; and (4) free education for all children in public schools; abolition of child factory labor in its present form; combination of education with industrial production.

And here in the good ol' US of A, we have: (1) the right to own land - but zoning laws and rent controls radically infringe on our right to use land; (2) a Federal Government with exclusive rights to issue and determine the value of money; (3) an Interstate Commerce Act (1887) and Civil Aeronautics Act (1938) which grant the Federal Government centralized control of surface and air transportation; and (4) a "free" public school system which most children attend.

Clearly, Marxist socialism has made serious inroads in the United States.

12. As the average ACT of Drury students goes up, the percentage of students who join a Greek organization goes down.

/.. Smart kids don't "go Greek."