We have seen that some invalid arguments may be good, and some may be bad, depending on whether the premises adequately support the conclusion. Similarly, while some valid arguments may be good, not all valid arguments are good arguments. Those with clearly false premises are bad, of course. However, there are some particular arguments that seem to have a valid form and possibly true premises, but, upon examination of the content of the argument, clearly exemplify errors in reasoning.
Straw Man: This is an argument attacking another person's argument. Often, when debating a point with another, it is wise to reconstruct the other person's argument in your own words. This ensures that you understand the argument, and can help you evaluate it. We often do this in class with the readings for the day; after all you cannot criticize someone's argument until you understand exactly what it is. The straw man fallacy occurs when you misrepresent the other person's argument, or a statement made by the other person, in a way that makes it much easier to criticize his or her argument.
Argument against the person (Ad hominem fallacy): This is also an argument against the conclusion of another person's argument. The conclusion of the argument is that the other person is wrong, but the premises of the argument, instead of giving good reasons not to believe the claim itself, attack the other person's character, intelligence, or motivation. In general statements about a person have nothing to do with whether that person's argument is valid, sound, strong, etc.
Appeal to the People: This is an argument in which the basis for the conclusion is the desire or need to be accepted or valued by a larger group. Unless there are specific reasons given to the contrary (as in scientific inquiry, for example), the fact that some group of people believe a statement (or supposedly believe a statement), is not an indication that the statement is true.
Appeal to Ignorance: This is an argument in which the basis for believing the truth of a statement is that its falsity has not been proven. Unfortunately, the converse argument seems just as persuasive: believing a statement is false merely because its truth has not been proven. Again, unless there are specific reasons given to the contrary, lack of proof for (or against) a statement does not constitute proof that the statement is false (or true).
Equivocation: This fallacy is made when an argument has a valid form, but in fact two or more meanings of a single word or phrase are used when validity depends on using just one meaning.
Begging the Question: This fallacy is also made when an argument has a valid form, but in fact the conclusion is merely a restatement of one or all of the premises. That is, begging the question occurs when one is assuming (using as a premise) that which is to be proven (the conclusion).
False Dilemma: This is another fallacy made when the argument has a valid form, but one of the premises is unfairly narrowing the possibilities to be considered. It usually occurs when someone asserts a dilemma (either A or B, with the implicit assumption that nothing other than A or B could be the case), but the fallacy can also occur for an assertion of three, four or more choices (as in: either A, B, or C, with the implicit assumption that nothing other than A, B, or C could be the case).
Appeal to Unreliable Authority: Generally, an appeal to authority can make a very strong (in the technical sense) argument for a particular conclusion. However, this is only true when the authority appealed to is actually a reliable source of information about the subject. This fallacy occurs when the source cited as a reason to believe a claim is either (1) not actually a reliable authority, (2) a reliable authority on some subjects, but not the one in question, or (3) is asserting a claim that is quite controversial even among reliable authorities in the field.
False Cause: This fallacy occurs when the claim is made that one possible cause of a phenomenon is a (or the) cause of another phenomenon without evidence excluding other possible causes. This fallacy comes in two common forms. The first is post hoc ergo propter hoc ("after this, therefore because of this"). This fallacy occurs when A is asserted to be the cause of B solely because A occurred before B. The second form is the slippery slope. This fallacy occurs when A is asserted to inevitably cause B, through some sort of chain reaction, despite lack of evidence that each link in the chain will inevitably lead to the next link.