When debating any number of reasons may be given in support or against an idea. A thorough understanding of the topic and context is, of course, incredibly useful. However, certain arguments are weak or even illegitimate. Logical fallacies may superficially sound compelling, but use poor reasoning and often cite irrelevant points. Therefore, familiarity with common fallacies can help you quickly identify when an assertion is weak and possibly wrong. Below are a few fallacies frequently employed by distant relatives on Facebook.
Ad Hominem: Rather than addressing the actual issue at hand, people often shift the focus to the person whom with they disagree. This is frequently employed to dismiss the views of members of an opposing political party. So, instead of actually rejecting an idea based on its merits, one will simply say, "I don't like that person" or "They are a liar". Now it is possible the person has been frequently caught lying, but in an of itself that doesn't mean that their argument is wrong.
Argument from Authority: In some ways this is the reverse of an Ad Hominem attack. Instead of rejecting an argument based on the person espousing it, one asserts it must be true because of their identity. The authority figure could be your mother (that said mothers are usually right), a boss, the President, or a religious leader. This doesn't mean that you should reject what experts say when they are speaking about something in their field. However, you might want to look closer if tax attorney starts going on about cutting gluten from your diet, but don't argue with him when he advises against a certain deduction. To differentiate between expert and non-expert you might have to look into a bit closer. If their degree is honorary, bad sign, or from an Ivy League school, good sign.
Emotional Appeal: This tactic includes F.U.D. (Fear Uncertainty and Doubt). Whenever someone is trying to scare you into a course of action, stop and think about things. Now if they have some data to backup why you shouldn't eat at that cheap sushi place, like previous health code violations, maybe you should go somewhere else for dinner. In situations like this channel your inner Spock and think logically rather than being swept up in the moment.
Ad Populum: George Carlin said, "Never underestimate the power of stupid people in large groups" and "Think about how stupid the average person is, and then realize that half of 'em are stupider than that." Therefore, one should never accept an argument simply because many other people accept it. My mom summarized this fallacy with the saying, "If all your friends were jumping off a bridge...would you do the same?" Once again, this doesn't mean you should reject an idea when a majority of experts support a position.
Argument from Antiquity: Also known as appeal to tradition, this fallacy insists we continue acting in a certain way because that is how we have always acted. Alternatively, people may suggest ancient civilizations possessed some knowledge now lost or that modern man is behaving in a manner at odds with our biology. For examples look at fad diets (Paleo, gluten-free) or those silly toe shoes. Just remember that bloodletting accounted for 80% of medicine for several thousand years. Humans tend to gain knowledge and improve over time. I'll stick with the newest, latest, and best.
Straw Man: This tactic either targets the weakest argument of an opponent or grossly misrepresents their position. From there one has a much easier task of refuting an exaggerated or compromised assertion. This can be combined with cherry picking, the practice of ignoring the majority of evidence and focusing on only that which is in line with one's beliefs, regardless of quality. This process can give the impression of a confrontation while actually ignoring it.