Powerful speakers use confidence and self assurance, a quick flow of words and a cutting and acerbic manner to establish themselves as experts and leaders. Too often, their views are internally inconsistent and their arguments flawed.

In my life, I’ve been frustrated in too many bad arguments. As I’ve grown older, I have learned to pick apart the ideas of others and throw back some ideas of my own but it has been a slow process.

One of the most helpful resources I have found of late, are tools of logic and rhetoric which date back to classical times. These tools have been lost from mainstream curriculum but in my view they should every school child should learn to argue clearly and with integrity.

Here are a few types of bad arguments as identified by classical rhetoricians and logicians:

• Argumentum ad antiquitatem or the “argument to antiquity or tradition”. Best known as, “it’s always been done that way,” this argument is favoured by the establishment. While tradition should be honoured, it does not immediately make it the best course of action.
• Argumentum ad hominem or “argument directed at the person”. This means attacking the character or motives of a person who has stated an idea, rather than the idea itself.  For example,”We all know Nixon was a liar and a cheat, so why should we believe anything he says?” The relevant question is not who makes the argument, but whether the argument is valid.
• Argumentum ad ignorantiam or “argument to ignorance”. This means assuming something is true simply because it hasn’t been proven false. For example, someone might argue that global warming is certainly occurring because nobody has demonstrated conclusively that it is not. But failing to prove the global warming theory false is not the same as proving it true. This  depends crucially upon the burden of proof.
• Argumentum ad logicam or “argument to logic”. This means assuming that something is false simply because a proof or argument that someone has offered for it is invalid; this reasoning is wrong because there may be another proofs or arguments that successfully supports the proposition.
• Argumentum ad misericordiam or “argument or appeal to pity”. For example: “Think of all the poor, starving Ethiopian children! How could we be so cruel as not to help them?” It is, of course, perfectly legitimate to point out the severity of a problem as  justification for  a proposed solution. The problem comes in when other aspects of the proposed solution -such as whether it is possible, how much it costs, who else might be harmed by adopting the policy- are ignored or responded to only with more impassioned pleas.
• Argumentum ad nauseam or “argument to the point of disgust”; i.e., by repetition. This means trying to prove something by saying it again and again. Of course, it is not a fallacy to state the truth again and again; what is fallacious is to expect the repetition alone to substitute for real arguments.
• Argumentum ad numerum or “argument or appeal to numbers”. This neans proving something by showing how many people think that it’s true. For example: “At least 70% of all Americans support restrictions on access to abortions.” Well, maybe 70% of Americans are wrong!
• Argumentum ad populum or “argument or appeal to the public”. Like the appeal to numbers, this entails trying to prove something by showing that the public agrees with you.
• Argumentum ad verecundiam or “argument or appeal to authority”. This occurs when someone tries to demonstrate the truth of a proposition by citing some person who agrees, even though that person may have no expertise in the given area. For instance, some people like to quote Einstein’s opinions about politics (he tended to have fairly left-wing views), as though Einstein were a political philosopher rather than a physicist.

• Circulus in demonstrando or “circular argument”. Circular argumentation occurs when someone uses what they are trying to prove as part of the proof of that thing. For example,  “Marijuana is illegal in every state in the nation. And we all know that you shouldn’t violate the law. Since smoking pot is illegal, you shouldn’t smoke pot. And since you shouldn’t smoke pot, it is the duty of the government to stop people from smoking it, which is why marijuana is illegal!”
• Complex question. A complex question is a question that implicitly assumes something to be true by its construction, such as “Have you stopped beating your wife?” A question like this is fallacious only if the thing presumed true (in this case, that you beat your wife) has not been established.
• Cum hoc ergo propter hoc or “with this, therefore because of this”. This is the familiar thinking that because two things occur simultaneously, one must be a cause of the other.  For example, “President Clinton has great economic policies; just look at how well the economy is doing while he’s in office!” These two things may happen at the same time merely by coincidence.
• Dicto simpliciter or “spoken simply”, i.e., sweeping generalization. This means making a sweeping statement and expecting it to be true of every specific case — in other words, stereotyping. Example: “Women are on average not as strong as men and less able to carry a gun. Therefore women can’t pull their weight in a military unit.” The problem is that the sweeping statement may be true (on average, women are indeed weaker than men), but it is not necessarily true for every member of the group in question (there are some women who are much stronger than the average).
• Nature, appeal to. This entails the assumption that whatever is “natural” or consistent with “nature” (somehow defined) is good, or that whatever conflicts with nature is bad. For example, “Homosexuality is unnatural; it is not the evolutionary function of sexual intercourse. Therefore it is wrong.” After all, wearing clothes, tilling the soil, and using fire might be considered unnatural since no other animals do so, but humans do these things all the time and to great benefit.

• Naturalistic fallacy. This is trying to derive conclusions about what is right or good (that is, about values) from statements of fact alone. For example, someone might argue that the premise, “This medicine will prevent you from dying” immediately leads to the conclusion, “You should take this medicine.” But this reasoning is invalid, because the former statement is a statement of fact, while the latter is a statement of value. To reach the conclusion that you ought to take the medicine, you would need at least one more premise: “You ought to try to preserve your life whenever possible.”
• Non Sequitur or “It does not follow”. This is simply stating, as a conclusion, something that does not strictly follow from the premises. For example, “Racism is wrong. Therefore, we need affirmative action.” Obviously, there is at least one missing step in this argument, because the wrongness of racism does not imply a need for affirmative action without some additional support (such as, “Racism is common,” “Affirmative action would reduce racism,” “There are no superior alternatives to affirmative action,” etc.).
• Petitio principii or “begging the question”. This entails making the assumption when trying to prove something, what it is that you are trying prove. If somebody said, “The fact that we believe pornography should be legal means that it is a valid form of free expression. And since it’s free expression, it shouldn’t be banned,” that would be begging the question. This is also a circular argument.
• Post hoc ergo propter hoc or “after this, therefore because of this”. This entails the assumption that A caused B simply because A happened prior to B. A favorite example: “Most rapists read pornography when they were teenagers; obviously, pornography causes violence toward women.” The conclusion is invalid, because there can be a correlation between two phenomena without one causing the other.
• Red herring. This entails  irrelevant facts or arguments to distract from the question at hand. For example, “The opposition claims that welfare dependency leads to higher crime rates — but how are poor people supposed to keep a roof over their heads without our help?” It is perfectly valid to ask this question as part of the broader debate, but to pose it as a response to the argument about welfare leading to crime is fallacious.
• Slippery slope. A slippery slope is an argument that says adopting one policy or taking one action will lead to a series of other policies or actions also being taken, without showing a causal connection between the advocated policy and the consequent policies. A popular example of the slippery slope fallacy is, “If we legalize marijuana, the next thing you know we’ll legalize heroin, LSD, and crack cocaine.” This is a form of non sequitur if no reason has been provided for why legalization of one thing leads to legalization of another.
• Straw man. This is the mistake to argue against a caricatured or extreme version of somebody’s argument, rather than the actual argument they’ve made. Often this fallacy involves putting words into somebody’s mouth by saying they’ve made arguments they haven’t actually made. For example, if Pauline Hanson expresses a desire to keep Australian values by limiting immigration, an opponent may argue that Pauline Hanson supports a white-Australia policy and is xenophobic.
• Tu quoque or “you too”. This entails defending an error in one’s reasoning by pointing out that one’s opponent has made the same error. For example, “They accuse us of making unjustified assertions. But they asserted a lot of things, too!”

These points were summarised from a resource of Glen Whitman, Associate Professor of Economics at California State University.