Post hoc ergo propter hoc.. That's Latin for "After this, therefore because of this." It's the official name for a common logical error; e.g., Joe breaks a mirror and six months later gets fired, so Bob concludes the mirror must have caused the firing.

Of course, Bob's conclusion is unsupported. (The mirror could have been the cause, but there is no evidence given to show this.) If Bob had only known about the post hoc error, he could have avoided embarrassment, ridicule and paranoia about mirrors. In t hat spirit, I would like to outline some of the more egregious logical errors I've come across, complete with real-life examples. Clip and save this as a handy reference for any essays, papers or letters to the editor you may write.

• Failing to see the full implications of a statement. This one happens all the time. It often comes up when someone tries to prove a specific point with a vast, false generalization, as in "Drugs should be legal because the government can't tell us what to do," or "Gays should be in the military because free people have the right to do as they damn please" (due to former thinker Mr. Barry Goldwater). You can easily use this error to box an opponent into a contradiction; e.g., "If free people can do as they please, then I can take your wallet, like this."

  (Sometimes, in fact, the opponent will do this for you. My favorite example: "We don't have the right to judge other people, and therefore John Keisling is a rotten S.O.B. because he does it!" The Diversity Action Program's Mission Statement is the same w ay.)

• Confusing ethics with law. A classic example is the Roe v. Wade dodge, in which pro-choice apologists go to great lengths to show that abortion is legal. The issue, though, is whether it ought to be legal; that is, whether it is m orally acceptable. Contradiction trap: Slavery was legal for decades, but that did not make it right.

• The "personal experience" fallacy. This is thinking that one cannot make a judgment unless he has personally experienced what he is judging (e.g., welfare). The premier example is gay rights: "You can't say it's wrong because you don't know what it's like to be gay." Counterexample: pedophilia. We can indeed say it's wrong even without ourselves having felt pedophilic urges.

• Thinking that seemingly unrelated events cannot have the same cause. Example: Attacking the Christian Coalition by saying, "I don't believe that if we outlawed abortion, crime would just go away." Well, no; it wouldn't. But if outlawing abortion had the goal of restoring the sanctity of human life, then violent crime might indeed decrease. Very different events; same root cause.

• Refusing to move from the general to the particular. It's true that one cannot go from the specific to the general. But one can go the other way. Example: If I prove that atheism is no more empirically likely to be true than any other religion, then in particular, it's no more likely to be true than Christianity. Education specialists, take note.

• The "total effect opposition" fallacy, or, the "NRA hates cops" mistake. (The names are my own.) Here's the flawed logic, from an actual (!) letter to the editor. Banning handguns will mean fewer cops killed. (Debatable, but granted.) The NRA opposes a handgun ban. Therefore, the NRA must want those extra cops dead!

  Flaw: The NRA could (and does) oppose the ban for its other, negative effects. An analogy: Suspending the Constitution and giving police absolute power would also save cops' lives. The ACLU opposes such a move. Does this mean the ACLU wants cops to die?

  To close, I cannot resist a few personal facts, just to shatter any stereotypes about right-wingers. I lived in Panama as an army brat for 8 years, traveling widely in Panama, Peru, the Galapagos and Uruguay. I know French, Spanish and Latin. I have impersonated Elvis - singing with a mike in full costume - professionally. I have acted in over 25 productions and taken one semester each of tap, jazz and ballet. A hopeless romantic, I own the Bed of Roses soundtrack, a 9mm semiautomatic, a Batman Forever tie and a calendar of those Kim Anderson photos of kids playing dress-up. I am race-blind in all affairs except theatrical casting. Lastly, I have imitated Jim Carrey while teaching class, twice. If that doesn't make me a right-wing maverick, I don't know what will.

John Keisling's new book, a collection of his 54 Wildcat columns plus nine others, is available TODAY, in the Student Union Arcade (across from the Fiddlee Fig) from 11 a.m. to 2 p.m.! Go there now, or e-mail keisl@math.arizona.edu, or call 325-0351 .