what is the fallacy of the argumentum ad hominem
That it is not always fallacious, and that in some instances, questions of personal conduct, character, motives, etc., are legitimate and relevant to the issue, as when it directly involves hypocrisy, or actions contradicting the subject's words.
Ad hominem
Walton has argued that "ad hominem" reasoning is not always fallacious, and that in some instances, questions of personal conduct, character, motives, etc., are legitimate and relevant to the issue, as when it directly involves hypocrisy, or actions contradicting the subject's words.

The philosopher Charles Taylor has argued that "ad hominem" reasoning (discussing facts about the speaker or author relative to the value of his statements) is essential to understanding certain moral issues due to the connection between individual persons and morality (or moral claims), and contrasts this sort of reasoning with the apodictic reasoning (involving facts beyond dispute or clearly established) of philosophical naturalism.
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Ad hominem [SEP] Criticism as a fallacy
Walton has argued that "ad hominem" reasoning is not always fallacious, and that in some instances, questions of personal conduct, character, motives, etc., are legitimate and relevant to the issue, as when it directly involves hypocrisy, or actions contradicting the subject's words. The philosopher Charles Taylor has argued that "ad hominem" reasoning (discussing facts about the speaker or author relative to the value of his statements) is essential to understanding certain moral issues due to the connection between individual persons and morality (or moral claims), and contrasts this sort of reasoning with the apodictic reasoning (involving facts beyond dispute or clearly established) of philosophical naturalism.