(Excerpted from 42 Fallacies by Michael C. LaBossiere, 2nd Edition, 2013 Revision 2.1, ebook)

“Understanding what a fallacy is requires that you first have at least a basic understanding of arguments in the philosophical sense. In philosophy, an argument is not a fight or even a dispute. Rather, an argument is as set of claims (statements that can be true or false) that are related in a way that one of them is supported by the others. Another way to look at it is that one claim is presented to be proven and the other claims are presented as evidence or reasons for that claim.” (Page 1 of 85)

“If a deductive argument is such that the premises could all be true while the conclusion is false at the same time, then the argument is invalid. Invalid arguments are always unsound. This is because a sound argument must be valid and have all true premises.” (Page 2 of 85)

“Unfortunately for those who teach about fallacies, people often use the term “fallacy” when they are actually referring to a factual error. For example, someone might say “a lot of people think that Google created Android from scratch, but that is a fallacy. Google actually based Android on Linux.” While thinking that Android was created from scratch would be an error, it is an error about the facts, rather than an error in logic. If someone said “Android is awful. After all, a fair number of creepy geeks use it”, then this would be an error in logic. Even if creepy geeks use Android, this does not prove that the operating system is awful. While both of these are mistakes, they are two different types of mistakes.” (Page 3 of 85)

“So, a fallacy is an error in reasoning/ logic. To be more specific, a fallacy is an argument in which the premises fail to provide adequate logical support for the conclusion.” (Page 3 of 85)

“A fallacy is, very generally, an error in reasoning. This differs from a factual error, which is simply being wrong about the facts.” (Page 5 of 85)

“An ad Hominem is a general category of fallacies in which a claim or argument is rejected on the basis of some irrelevant fact about the author of or the person presenting the claim or argument. Typically, this fallacy involves two steps. First, an attack against the character of person making the claim, her circumstances, or her actions is made (or the character, circumstances, or actions of the person reporting the claim). Second, this attack is taken to be evidence against the claim or argument the person in question is making (or presenting).” (Page 7 of 85; Ad Hominem Fallacy)