I love logic. It asserts itself in wonderful ways in our lives and enriches the understanding of, well reality.
Knowing that, allow me to explain that logic isn't just 'being clever' or what have you. Logic has rules, rules needed so you can overcome some of the... not shortcomings, but small biases and mental shortcuts that the human brain is prone to.
Tonight we'll take a look at logical fallacies. There are two kinds, ones simply being wrong, having incorrect information, that sort of thing, and aren't touched on very frequently for obvious reasons. The other kind, formal fallacies (so named because the problem lies in the form of the argument regardless of its outcome) are a field of study unto themselves, and it's those we'll focus on.
First up is the Ad Hominem and this is the one you'll run into most often. It's latin for 'against the man' and like it sounds, its attacking the person instead of the argument. There are other forms of it, specialized cases: Reductio ad Hitlerum (not real latin) is the most famous of these and is the act of Godwinning an argument. Poisoning the Well, the act of pointing out damaging information about someone unrelated to their argument or proposal, is common as well, as much on our side as on the other but the easiest example is throwing 'socialist' in front of every Democratic proposal Fox has on the air. These are all fallacious arguments because attacking the carrier of an idea has no bearing on whether the idea itself is strong.
Next is the various appeals. Appeal to Authority, Appeal to Popularity, and their siblings. These all boil down to 'it's true because other people say it's true', either someone in an authoritative position (an expert an the subject, a political or spiritual leader) or sheer numbers of people (more people think X so you must be wrong). Arguments such as these are fallacious because it does not address or support the merits of the argument. Note, however, that not everything that seems to be covered by Appeal to Authority is always forbidden. In an argument about, say, climate change, or Rice growth patterns, or cheese, in which evidence from studies or other experiments is needed, it IS logically acceptable to use information from these sources as authoritative in terms of the veracity of the numbers used before you use them as well. This is different and still requires a formally correct argument to be taken forward based on those numbers/observations. These arguments are fallacious because they have zero effect or evidence one way or the other, they present no evidence in favor and offer no true detractions when used in opposition.
The Strawman comes along about now. A Strawman argument is a twisted, incorrect, or extended beyond the bounds of reason presentation of your opponents position that is frequently easier (or at least offers more dramatic possibilities) to argue against. Examples of this were seen frequently in the run up to health car with the 'if you support this bill you support death panels and rationing and killing Granny'. These arguments are fallacious because you're addressing a different question then the one presented to you.
Special Pleading is an argument of exception. It's involved a lot in alternative 'medicine' but gets into politics enough for it to be useful here. Say Senator X takes a tough stand on drunk driving, arguing that it should be a mandatory minimum sentence of 5 years. All good so far. Senator get's caught drunk driving. The argument for Special Pleading would come into play if he then argued for special circumstances or conditions that exempted him. Homeopathy and Acupuncture get caught up in this when its shown they aren't any more effective then a placebo and then try to take credit for the placebo effect, a special pleading of health science that must show efficacy above the placebo effect. A related fallacy is Moving the Goalposts where whenever something is shown, the point being argued is moved back (or sideways) slightly. An evolution denier will walk this slope a lot, with every new piece of information the goalposts get moved slightly, always just beyond what a fossil has shown. These arguments are fallacious because they seek to hide or wall off an argument from valid criticism.
Post hoc Rationalization or Post hoc ergo propter hoc (After this, therefore because of this). Also colloquially remembered with 'Correlation is not Causation' it covers a mental shortcut animals (including humans) have developed that takes significantly less brain time and brain power then actually examining things. When something happens, and is followed by something else, we assume its because of the first thing when in reality all we know is there were correlated. One could actually be caused by the other, they could be unrelated, or they could both be caused by an otherwise unknown other thing. You complain of a headache. Friend tells you to drink more water because they drink a bunch of water and never get a headache. the two could be utterly unrelated (he gets no headaches for other reasons and likes drinking water), have a causality link (headaches are from dehydration and drinking water gets rid of them) or both be caused by a third thing (he drinks all that water because he keeps close tabs on what he eats and drinks for health reasons and because of that gets no headaches). You have no way of knowing which is correct and there is no data or evidence in the fallacy and as such the argument is fallacious.
False Dichotomy, or False Dilemma presents an argument as between a narrow set of options when in reality a much fuller set is possible. If I say 2+2=5, and you say 2+2=6 and we sit down and work out my problem, we see it's not correct. 2+2!=5. Hah, you shout, thinking you have won because you proved 2+2=5 is wrong. The argument is fallacious because while you proved me wrong, you did not actually advance any evidence in support of your argument (2+2=6), although you did effectively show I was wrong.
That's it for tonight, and most of the big ones have been covered. I'll pop in with a second part tomorrow covering the more minor fallacies and collecting a few real world examples to show off, maybe even see if anyone in the comments can recognize them without highlighting or the like. A better, more complete argument is how you win, and that's what we should always strive for: winning.