The fallacy of circumstantial ad hominem occurs when bias is presumed to follow necessarily from a person's situation, role, or job. This is usually combined with the fallacy of appeal to motive to dismiss the opinion of that person.

Here is an example:

Pav: "Bern hates the new business tax proposal. Should we consider his opinion?"

Len: "Heck No! Bern is a wealthy businessman, so of course he's going to be against any new business taxes."

The problem here is that there is no way to know if Bern really hates all new business taxes just because he is active in business. And even if he does, Bern could still have valid arguments against the new proposal. In fact, it may be precisely because of his business experience that he can understand unintended consequences of the tax, such as loopholes that would let some businesses dodge it, or predictable business countermoves like off-shoring of business deals. The only logical response to Bern's opposition is to leave his motives aside and examine his arguments on their merits.

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