Ad hominem abusive
Ad hominem abusive (also called argumentum ad personam) usually and most notoriously involves insulting or belittling one's opponent, but can also involve pointing out factual but ostensibly damning character flaws or actions which are irrelevant to the opponent's argument. This tactic is logically fallacious because insults and even true negative facts about the opponent's personal character have nothing to do with the logical merits of the opponent's arguments or assertions.
This tactic is frequently employed as a propaganda tool among politicians who are attempting to influence the voter base in their favor through an appeal to emotion rather than by logical means, especially when their own position is logically weaker than their opponent's. Another example is calling conspiranoia to a conspiracy theory that one does not like.
Examples:
* "You can't believe Jack when he says God exists because he doesn't even have a job."
* "Candidate Jane Jones's proposal X is ridiculous. She was caught cheating on her taxes in 2003."
Ad hominem circumstantial
Ad hominem circumstantial involves pointing out that someone is in circumstances such that he is disposed to take a particular position. Essentially, ad hominem circumstantial constitutes an attack on the bias of a source. The reason that this is fallacious in syllogistic logic is that pointing out that one's opponent is disposed to make a certain argument does not make the argument, from a logical point of view, any less credible; this overlaps with the genetic fallacy (an argument that a claim is incorrect due to its source).
On the other hand, where the source taking a position seeks to convince us by a claim of authority, or personal observation, observation of their circumstances may reduce the evidentiary weight of the claims, sometimes to zero.[4]
Examples:
* "Tobacco company representatives should not be believed when they say smoking doesn't seriously affect your health, because they're just defending their own multi-million-dollar financial interests."
* "He's physically addicted to nicotine. Of course he defends smoking!”
* "What do you know about politics? You're too young to vote!"
Mandy Rice-Davies's famous testimony, during the Profumo Affair, "Well, he would [say that], wouldn't he?", is an example of a valid circumstantial argument. Her point is that since a man in a prominent position, accused of an affair with a callgirl, would deny the claim whether it was true or false, his denial, in itself, carries little evidential weight against the claim of an affair. Note, however, that this argument is valid only insofar as it devalues the denial; it does not bolster the original claim. To construe evidentiary invalidation of the denial as evidentiary validation of the original claim is fallacious (on several different bases, including that of argumentum ad hominem); however likely the man in question would be to deny an affair that did in fact happen, he could only be more likely to deny an affair that never did.
Ad hominem tu quoque
Ad hominem tu quoque (lit: "You too!") refers to a claim that the source making the argument has spoken or acted in a way inconsistent with the argument. In particular, if Source A criticizes the actions of Source B, a tu quoque response is that Source A has acted in the same way.
Examples:
* "You say that stealing is wrong, but you do it as well."
* "He says we shouldn't enslave people, yet he himself owns slaves"
[edit] Guilt by association
Main article: Association fallacy
Guilt by association can sometimes also be a type of ad hominem fallacy, if the argument attacks a source because of the similarity between the views of someone making an argument and other proponents of the argument.
This form of the argument is as follows:
Source A makes claim P.
Group B also make claim P.
Therefore, source A is a member of group B.
Example:
"You say the gap between the rich and poor is unacceptable, but communists also say this, therefore you are a communist"
This fallacy can also take another form:
Source A makes claim P.
Group B make claims P and Q
Therefore, Source A makes claim Q.
Examples:
"You say the gap between the rich and poor is unacceptable, but communists also say this, and they believe in revolution. Thus, you believe in revolution."
A similar tactic may be employed to encourage someone to renounce an opinion, or force them to choose between renouncing an opinion or admitting membership in a group. For example:
"You say the gap between the rich and poor is unacceptable. You don't really mean that, do you? Communists say the same thing. You're not a communist, are you?"
Guilt by association may be combined with ad hominem abusive. For example:
"You say the gap between the rich and poor is unacceptable, but communists also say this, and therefore you are a communist. Communists are unlikeable, and therefore everything they say is false, and therefore everything you say is false."
A reductio ad Hitlerum argument can be seen as an example of a "guilt by association" fallacy, since it attacks a viewpoint simply because it was supposedly espoused by Adolf Hitler, as if it is impossible that such a man could have held any viewpoint that is correct.
Inverse ad hominem
An inverse ad hominem argument praises a source in order to add support for that source's argument or claim. A fallacious inverse ad hominem argument may go something like this:
"That man was smartly-dressed and charming, so I'll accept his argument that I should vote for him"
As with regular ad hominem arguments, not all cases of inverse ad hominem are fallacious. Consider the following:
"Elizabeth has never told a lie in her entire life, and she says she saw him take the bag. She must be telling the truth."
Here the arguer is not suggesting we accept Elizabeth's argument, but her testimony. Her being an honest person is relevant to the truth of the conclusion (that he took the bag), just as her having bad eyesight (a regular case of ad hominem) would give reason not to believe her. However, the last part of the argument is false even if the premise is true, since having never told a lie before does not mean she isn't now.
Appeal to authority is a type of inverse ad hominem argument.
I truly am interested in a constructive exchange of ideas. We all need to think before we press that send button.