Causality: Avoid the blunder of asserting a causal relationship with the popular fallacy of post hoc ergo propter hoc which declares that because some event A happened and immediately afterward event B happened that event A was the cause of event B.  (I knew someone whose car stalled on the way to work.  She would get out and open the hood and slam it and then the car would start.  Singing a song would have been just as effective to allow time for a vapor lock to dissipate!) Also avoid the popular fallacy that correlation proves causation.  People who own Cadillacs, on average, have higher incomes than people who don't.  This does not mean that if we provided people with Cadillacs that they would have higher incomes.

Innuendo: Innuendo is saying something pejorative about your opponent without coming right out and saying it but by making more or less veiled allusions to some circumstance, rumor, or popular belief. If you want to see some excellent examples of innuendo, watch Rush Limbaugh. Politicians are, unfortunately, frequently guilty of using innuendo. It is an easy way to capitalize on popular prejudices without having to make explicit statements which might be difficult or impossible to defend against rational attack.

Be sure of your facts.  What is the source of your information?  If it is a newspaper or a magazine, are you sure that the information hasn't been "slanted" to agree with that publication's political bias?  Where crucial facts are concerned, it is best to check with more than one source.  Often international publications will give you a different perspective than your hometown newspaper. Check to see whether the book you are using was published by a regular publishing company or whether it was published by some special interest group like the John Birch Society or a religious organization. These books cannot be trusted to present unbiased evidence since their motivation for publishing is not truth but rather the furtherance of some political or religious view.

Understand your opponents' arguments.  It is good practice to argue with a friend and take a position with which you do not agree.  In this way you may discover some of the assumptions your opponents are making which will help you in the debate.  Remember that everybody thinks that his position is the right one, and everybody has his reasons for thinking so.

Do not impute ridiculous or malevolent ideas to your opponent.  An example of this is the rhetorical statement, "Have you stopped beating your wife?" This imputes or presupposes that your opponent has beaten his wife. One frequently sees references by conservative speakers and writers to the idea that gay activists want "special privileges." This would be ridiculous if it were true. It isn't true, but speaking as if it were true and well known to all is egregiously unfair to listeners or readers who may not be well informed. It is probably always wise to treat your opponent with respect, even if he doesn't deserve it. If he doesn't deserve respect, this will probably soon become obvious enough. There are all sorts of subtle ways to express hostility toward your opponent and it is almost always unwise to give in to them. That doesn't mean that you can't vividly and saliently present your criticisms of your opponent's beliefs or behavior. But beware of phraseology which simply makes him look ridiculous. An example of this came up recently. I was criticizing Pat Robertson's apparent belief that God punishes people who do not behave as he wants them to by sending storms or natural disasters of various kinds or even terrorists. I do think this is a childish and obviously invalid belief. Saying so is not a violation of any of the principles enumerated here. But I found myself saying that Pat Robertson's "Big Friend in the Sky" would do such and so. This is objectionable because it ridicules. It isn't as straightforward as simply saying that in my opinion Pat Robertson's belief is ridiculous. Another example is to say that nudists "prance around" in the nude. Of course it's inaccurate, but it ridicules and denigrates as well and shouldn't be allowed in a rational debate.

Regression to the mean:  Another source of error which occurs very frequently is the failure to take into account regression to the mean. This is a bit technical, but it is very important, especially in any kind of social or psychological research which depends upon statistical surveys or even experiments which involve statistical sampling. Rather than a general statement of the principle (which becomes more and more unintelligible as the statement becomes more and more rigorous) an example will be used. Let's consider intelligence testing. Perhaps we have a drug that is supposed to raise the IQ of mentally retarded kids. So we give a thousand intelligence tests and select the 30 lowest scoring individuals. We then give these low scoring kids our drug and test them again. We find that there has been an increase in the average of their IQ scores. Is this evidence that the drug increased the IQ? Not necessarily! Suppose we want to show that smoking marijuana lowers the IQ. Well, we take the 30 highest scoring kids in our sample and give them THC and test them again. We find a lower average IQ. Is this evidence that marijuana lowers the IQ? Not necessarily! Any statistician knows that if you make some kind of a measurement of some attribute of a large sample of people and then select the highest and lowest scoring individuals and make the same measurement again, the high scoring group will have a lower average score and the low scoring group will have a higher average score than they did the first time. This is called "regression to the mean" and it is a perfectly universal statistical principle. It has nothing to do with what is being measured. It works with molecules and atoms just as it does with juvenile delinquents and schizophrenics. What is going on here? The whole thing is based on the fact that when we measure something there is always a bit of luck involved. Sometimes this is called "chance". Statisticians call it "error". There are two kinds of luck: good and bad. Let's say you take an IQ test and score 130. That's pretty good, considering that the average IQ is 100. What part of your score is luck? Well, there's no way of knowing this, but we know that some luck was involved. Is it more likely that your true IQ is 129 but that you had enough good luck to make it 130, or that your true IQ is 131 and that you had enough bad luck to make it 130? Well, there are a lot more people whose true IQ is 129 than there are people whose true IQ is 131, so there are more ways to get 130 because of good luck than there are ways to make 130 because of bad luck. If you have understood this, go to the head of the class! But even if you haven't understood it completely, remember it. Failure to understand it has probably cost us billions of dollars. Another important fact about regression to the mean is that the less reliable the measurement is the more regression will occur.

There are undoubtedly more points to be made here.  Suggestions will be gratefully received. Larry has made the following suggestions:

• Apply the scientific method.
  
• Cite relevant personal experience.
  
• Be polite.
  
• Organize your response. (Beginning, middle, end.)
  
• Treat people as individuals. (Not everyone who is pro-choice is also anti-gun.)
  
• Cite sources for statistics and studies used.
  
• Literacy works. Break posts into sentences and paragraphs.
  
• Read the post you are responding to.
  
• Stay open to learning.
  

And DWA has reminded us that Carl Sagan had a "baloney detection kit." Here it is:

• Wherever possible there must be independent confirmation of the facts
  
• Encourage substantive debate on the evidence by knowledgeable proponents of all points of view.
  
• Arguments from authority carry little weight (in science there are no "authorities").
  
• Spin more than one hypothesis - don't simply run with the first idea that caught your fancy.
  
• Try not to get overly attached to a hypothesis just because it's yours.
  
• Quantify, wherever possible.
  
• If there is a chain of argument every link in the chain must work.
  
• "Occam's razor" - if there are two hypotheses that explain the data equally well choose the simpler.
  
• Ask whether the hypothesis can, at least in principle, be falsified (shown to be false by some unambiguous test). In other words, is it testable? Can others duplicate the experiment and get the same result?
  

Additional issues are :

• Conduct control experiments - especially "double blind" experiments where the person taking measurements is not aware of the test and control subjects.
  
• Check for confounding factors - separate the variables.
  

Common fallacies of logic and rhetoric:

• Ad hominem - attacking the arguer and not the argument.
  
• Argument from "authority".
  
• Argument from adverse consequences (putting pressure on the decision maker by pointing out dire consequences of an "unfavourable" decision).
  
• Appeal to ignorance (absence of evidence is not evidence of absence).
  
• Special pleading (typically referring to god's will).
  
• Begging the question (assuming an answer in the way the question is phrased).
  
• Observational selection (counting the hits and forgetting the misses).
  
• Statistics of small numbers (such as drawing conclusions from inadequate sample sizes).
  
• Misunderstanding the nature of statistics (President Eisenhower expressing astonishment and alarm on discovering that fully half of all Americans have below average intelligence!)
  
• Inconsistency (e.g. military expenditures based on worst case scenarios but scientific projections on environmental dangers thriftily ignored because they are not "proved").
  
• Non sequitur - "it does not follow" - the logic falls down.
  
• Post hoc, ergo propter hoc - "it happened after so it was caused by" - confusion of cause and effect.
  
• Meaningless question ("what happens when an irresistible force meets an immovable object?).
  
• Excluded middle -considering only the two extremes in a range of possibilities (making the "other side" look worse than it really is).
  
• Short-term v. long-term - a subset of excluded middle ("why pursue fundamental science when we have so huge a budget deficit?").
  
• Slippery slope - a subset of excluded middle -unwarranted extrapolation of the effects (give an inch and they will take a mile).
  
• Confusion of correlation and causation.
  
• Straw man - caricaturing (or stereotyping) a position to make it easier to attack.
  
• Suppressed evidence or half-truths.
  
• Weasel words - for example, use of euphemisms for war such as "police action" to get around limitations on Presidential powers. "An important art of politicians is to find new names for institutions which under old names have become odious to the public" .
  

It has been pointed out by various participants that following these recommendations to the letter might make for dull reading. The idea is that a little invective is a good thing because it adds spice. An interesting example of this occurred in a nationally televised debate between Dan Quayle and Lloyd Benson. Quayle had just remarked on some similarities between himself and Jack Kennedy. Benson said, "I knew Jack Kennedy. Jack Kennedy was a friend of mine. But I can tell you one thing, Senator, you're no Jack Kennedy!" This was of course an argumentum ad hominem of the first water. But I would like to point out that a political debate and a scientific debate are two quite different things. But to concede the point somewhat I have a suggestion. Perhaps we could agree to divide our debating messages into two parts. In the first part it would be illegal to mention the opponent at all. The word "you" would be forbidden. Then the second part would allow judicious use of personal remarks. Writing a debate without using "you" is a very interesting exercise. I urge everyone to give it a try!

(Incidentally, the fugue you have been listening to if you clicked on the icon at the top of the page was chosen because a fugue can be thought of as a debate.  In this particular fugue there are three combatants represented by the three voices. There are notable discords sprinkled thoughout the fugue, but all is harmony at the end!)