Anyone who tries to argue a point is obligated to support assertions with well-reasoned evidence in the form of facts, statistics, illustrations and to support that assertion with reasonableness and logic. There are, however, several very common pitfalls—generally labeled fallacies in reasoning or logical fallacies—waiting for the unwary:
1. Argumentum ad hominem: essentially, an argument or attack on a person rather than the person’s idea. For example, a nationally-televised political commentator, who happened to get his start in show business as a comedian, spoke out against the “Don’t ask, don’t tell” policy, which is a way of circumventing the prohibition against homosexuals serving in the military but keeping that policy in force. One of the proponents of the policy said, “What could he possibly know about this? He’s a comedian!” Instead of focusing on whether the policy itself is good or bad, the speaker launched an attack on the person whose views he didn’t like, which set up a false target and ignored the real issue of disagreement.
2. Non sequitur: literally, “it does not follow.” During a campaign speech, one candidate said to the audience, “If we can land men on the moon, we can find a cure for cancer.” Landing men on the moon, of course, was a triumph of technology, skill, intellect and collective will, but the success of that endeavor has no logical connection to the effort it might take to conquer a disease as complicated and multi form as cancer. In other words, the ability to cure cancer does not follow logically from the ability to land men on the moon.
3. Post hoc: propter hoc—Latin for “after this, therefore because of it.” A simple explanation of this fallacy in logic might go like this: “I came down with a cold this morning. Last night, I went to a concert. I must have caught the cold at the concert.” The essential problem is that there is no logical causal connection between going to the concert and catching a cold.
4. Begging the question: offering as evidence something that needs to be proved is begging the question. Arguing that the car industry in the US is the best in the world, for example, a speaker might say, “Everyone knows that America makes the best cars in the world.” Although this statement might be true, it is not self-evidently true, and to be more than an assertion, such as statement would need to be supported with reasonable evidence.