Since argument is a large part of atheism, and life in general, we'll talk about a few major logic errors in argumentation every Friday. Being an atheist, I tend to argue a lot. These basic rules of rhetoric and argumentation are not strictly exclusive to atheists; these fallacies should be avoided by anyone trying to establish a correct, watertight argument. So if you're a theist, make sure you don't break these (and other) rules when defending your position. Ditto to you non-theists as well.
Not Followin' Ya
To get things started, we should cover the most basic type of fallacy of which most all others are a subset of: the non sequitur. Latin, it literally means "it does not follow". A big thing when dealing with logical progressions (ie, step-by-step argument) is that the conclusion must follow from the premise. I know, great idea, right? You'd be amazed at how Here's a few examples:
"Millions of people have seen unexplained lights in the night sky. Life on other planets is quickly becoming certainty."
"If I am in Tokyo, then I am in Japan. I am not in Tokyo. Therefore, I'm not in Japan."
Arguing at length, "My religion is of great help to many people." Then, concluding: "My religion is undoubtably true!"
If you're going to construct a chain of causation (A leads to B leads to C, etc.) without justifying each step in the chain, you're guilty of committing a non sequitur. For each step in the chain that you fail to justify, it will be obvious by the end that the alleged chain of causation is tenuous and implausible.
If have a habit of doing this, or you'd like to learn more about non sequiturs, Google is your friend. There are tons of sites on the internet that will show you how to avoid such errors in the future. If you can learn to argue without such incorrect reasoning, we atheists will be more likely to hear your position and, who knows, maybe even concede it!