Informal Logical Fallacies - Argumentum ad Hominem

 Argumentum ad hominem (usually just referred to ad Hominiem) is a logical fallacy in which an interlocutor's character, appearance, expertise and/or manners are maligned instead of directly addressing the truth or substance of their argument. For example:

Baldrick: I have a plan

Blackadder: Is it a cunning plan?

Baldrick: Yes it is a cunning and subtle plan

Blackadder: You wouldn't recognize a subtle plan if it painted itself purple and danced naked on a harpsichord while singing "subtle plans are here again"

Rather than discussing the merits, or otherwise, of Baldrick's plan, Blackadder just attacks Baldrick's intelligence.

Ad hominem translates as 'to the person' or 'against the person' and refers to the use of a personal attack instead of addressing the argument itself. Note that simply insulting someone (e.g. Donald Trump referring to 'Sleepy Joe' or Crooked Hilary' in one of his rambling speeches) is not an ad hominem fallacy unless the name calling is meant to discredit the opponent's argument.

There are 5 common types of ad hominem fallacies:

Abusive ad hominem: insulting a personal trait or characteristic such as 'What do you know about the offside rule in football, you're just a woman'.

Circumstantial ad hominem: also known as an appeal to motive where you criticize a person's perceived bias based on their job or situation. For example: 'Of course you believe in global warming so you can just get more grant money'.

Poisoning the well: this is where you get your character assassination in early before the discussion has started. For example: 'My opponent is going to argue against renewable energy because she works for an oil company'.

Guilt by association: an assumed bias by virtue of being a member of a particualar group or association. For example: 'You are against free choice for women because of your religious beliefs' or 'Your ideology is capitalism so obviously you want lower taxes'.

Tu quoque: translates as 'you, too' and is a form of ad hominem when used to imply your debate opponent is being hypocritical rather than addressing their argument. For example: 'How can you advocate for tougher drink/driving laws when you've been convicted for the same offence?'

The ad hominem fallacy is the worst form of rhetoric when used as an argument. There is no substance to the argument (i.e. no thought or intelligence) and it is completely devoid of logic or reason. It will, therefore, come as no surprise to discover that Donald Trump Jr is the world's leading proponent of this fallacy. Here are just three examples of many ...

In conclusion, you should always avoid using the argumentum ad hominem fallacy unless you want to come across as a low IQ unstable genius!

On a final point, describing a person's intelligence, position, credentials, etc is not an ad hominem fallacy if those traits and abilities are relevant to the discussion/argument. For example, if someone with no medical training is giving medical advice, then it is fair criticism to point out that fact without committing an ad hominem fallacy. On that basis, it is fair criticism to point out that someone who thinks a cognitive test for the onset of dementia is some form of IQ test is probably not the sharpest tool in the shed!