Definition:Argumentum ad Hominem

Definition

An argumentum ad hominem is a logical argument that concludes the falsehood of a statement because it is made by a particular person or group of people.

It can be argued that it is reasonable to be suspicious of an argument if:

most of the assertions made by said person or group regarding the topic under discussion are false

the person may have a vested interest in people believing an assertion made by that person.

However, such reasoning is still fallacious.

"I'm not even going to bother to read that proof you just posted up - if it's by you then it's bound to be rubbish."

"National Inquirer? Don't believe everything you read in there, those reporters are all crackpots."

"No butcher can be expected to argue honestly about the meat trade."

All of the above may or may not be true statements, but all are ultimately fallacious.