If I could make one course of study a required item in life, it would be logic.  In both FN and the world at large, thinking and arguing in a logical manner is critical to sound judgment and decision making.  Everyone should have a basic familiarity with logical thought, and should, at the very least, be able to recognize and avvoid illogical statements.  To that end, I am writing this admittedly incomplete intro to logical fallacies.  By avoiding these common errors, you can strengthen your TD arguments and your reasoning abilities in general.

There are formal (deductive) and informal (inductive) fallacies related to arguments.  TD are most often affected by informal fallacies.  They are fallacies related to inductive arguments, which, even if good, can potentially have true premises but a false conclusion.  Inductive arguments cannot be deductively proven, so it is left to the reasonability of the argument to show that the conclusion is most likely true.  These are the arguments we all make in TDs- not explicitly provable, but supportable.  And to support effectively, here's what we don't want to do.

COMMON INFORMAL FALLACIES OF RELEVANCE

RED HERRING:  This is when the arguer offers a distraction by diverting the argument from its focus by introducing another topic.  If you're aguring that Bill Walsh was a better coach than George Halas, don't start talking about Vince Lombardi.  Stay on target.  Trust me, that's something I know about.

AD HOMINEM ABUSIVE:  This is when the arguer attacks his or her opponent rather than addressing the argument.  If you're arguing that Brady is better than Manning and your opponent is from Indiana, don't attack him or her for living there- attack the weaknesses in his or her arguments instead.  Again, stay on target. 

FALLACY OF COMPOSITION: Another big one on FN- this is when the arguer asserts that the a whole must follow the same pattern as its parts.  If you're arguing about great baseball players don't say, "Lou Gehrig never led the league in strikeouts in any season, therefore he didn't strike out a lot."

GAMBLER'S FALLACY: This is where the arguer makes incorrect assumptions about odds.  Don't assume that a flipped coin that has come up with 5 straight heads will come up tails the next time- the odds are always 50-50.  This comes into play when we argue about a player being "due" for a good perfomance or a slump, or when we argue based on the "hot hand". 

BANDWAGON FALLACY:  This is when the arguer suggests that because something is commonly accepted, it must be true.  If you're arguing over who is the best shortstop, don't say "most people think Jeter is the best shortstop in baseball, therefore Jeter is the best".

WEAK ANALOGIES:  If you're going to compare to thigns, sports, or people, do it right.  Don't assume that because they are similar in one way that they are similar in another way.

IRRELEVANT APPEALS: There are all types of appeals that are not relevant to an argument.  Some common ones are:

• Appeal to authority- This is when an arguer argues based on a source rather than the strength of the statement.  Don't say that "the Dolphins will come back because Parcells says so" and expect that to be enough.  Citing an authority can be supportive, but it can't lead to a conclusion on its own. 
• Appeal to pity- Don't try to persuade by using emotional pleas.
• Appeal to force- Don't try to presuade with threats, e.g. "only an idiot would believe that LeBron is an MVP.  If you vote left, you're an idiot"
• Appeal to novelty or antiquity- Just because something is new and exciting or old and traditional doesn't make it true.  You see this a lot on FN when people argue about athletes from different eras.  Just because something is old and legendary doesn't mean it's better, but likewise, just because something is modern and cutting-edge doesn't mean it's better.
  
  

I know none of us should FN too seriously, but this is still good stuff to know.  If people find this helpful, I'll discuss fallacies of presumption next time. 

There are numerous resources on and offline that explain principles of logic in greater detail.  As an example, start here: http://www.logicalfallacies.info/