Logical failures - personal attacks

Argumentum ad hominem - personal attack

Argumentum ad hominem in literal translation is "argument aimed at man". There are two forms.
The first is the insulting form. If you refuse to accept an argument, and you justify your refusal by criticizing the person who made the argument, then you are guilty of an insulting personal attack. For example:
"You claim that atheists can be moral, but in fact I know you abandoned your wife and child"
This is a logical fallacy, because the truth of a claim does not depend on the qualities of the person making it. A less blatant form of this fallacy is to reject the claim based on the fact that the same claim was also made by another person who is easy to criticize. For example:
"...and therefore we have to close the synagogue? Hitler and Stalin would agree with you."
A second form of personal attack involves trying to convince the other person through the circumstances in which that person is. For example:
"...therefore there is no problem in killing animals for eating them. I hope you don't think otherwise, you seem to have no problem wearing leather shoes."
This is known as a circumstantial personal attack. This failure can be used as an excuse to reject the conclusion. For example:
"Of course you are against affirmative action. After all, you are male."
This specific form of personal attack, where you imply that some person came to a conclusion for their own selfish reasons, is also known as "poisoning the wells".
It is not always illegal to refer to the circumstances in which the person making the claim is correct. If someone is known to be a chronic liar, for example, then they will be considered a less reliable witness. Still, this does not mean that such a person's testimony is false in any case, and it certainly does not affect the legality of any logical argument he makes.

Tu quoque - but you too

This is the famous "you too" fallacy, in which you claim that a certain action is okay just because your discussion partner did it. For example:
"You're just arguing"
"So what? You also argued before"
This is a personal attack, and therefore a private case of the fallacy in this name.

Straw man - attacking an imaginary opponent

Also called the "straw man" fallacy, this fallacy occurs when you change someone else's position so that it is easier to attack, demolish the fallacious position, and then conclude that the original argument has failed. This is a logical fallacy because you did not deal with the actual arguments that were made.
"To be an atheist, you must know with absolute certainty that there is no God. To know this with absolute certainty, you must search the entire universe and all the places where God could be. Since it's clear and you didn't do it, then atheism is an impossible belief"
This argument, in various forms, appears about once a week online. If you do not see what is wrong with it, it is recommended to read the following document.

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