"I've never been able to understand women who say something controversial and then get all exercised when someone disagrees with them and dares to say so.” [ad hominem]
In my first creative writing class I was encouraged to avoid abstract Latinates—words derived from Latin roots—in favor of more concrete words. You’re telling a story and the reader wants a real concrete world to envision. But in discussing ideas, in argument, those old Latin and Greek abstract terms defining rhetorical devices are very useful.
When you write persuasively, for example, you need a thesis. And to make your point you probably need logos (logic), and maybe pathos (emotional appeal). You always need to establish your own ethos (your credibility as a writer). This is pretty basic stuff.
Ethos is served by a number of good writing habits such as careful supporting details—in fact skillful use of logic and emotion can serve to bolster ethos. Poor spelling and grammar, on the other hand, are rookie mistakes that undermine your writing.
It’s tempting, when you believe you have personal knowledge about a person that seems relevant to a discussion, to bring personal details or personality into the discussion. When debating responsibility in government, for example, you’re tempted to point out that your opponent was once careless himself with a campfire. Once in a while it works. Usually, in a discussion of issues, ideals, or societal goals, such personal attacks are an inappropriate detour. It’s called an ad hominem, or personal abuse or personal attacks. It ruins your argument and your credibility. It suggests you are weak, that you don’t really understand what you are discussing. You have no ethos.
I react with confusion to ad hominem when I’m on the receiving end, and I honestly do try to avoid using ad hominem in discussions. I’m sure I’ve failed, but usually I catch myself in time. A good argument is not a personal attack on another person, and should not be taken personally or directed toward a person.
When, instead of discussing the issue you attack the person you are talking to, you judge the person rather than the idea, you use that person’s life and actions rather than their reasoning to debate their points, you name-call rather than look for specific details in the discussion to . . . discuss—that’s probably ad hominem. It’s a sign of weakness to use ad hominem—it shows you don’t know what the heck you’re doing. Ad hominem is a sign of desperation. It’s rude, stupid, and you need to resist.
This matters because when an idea is properly debated, it is possible to discuss widely disparate points of view without getting tangled up in personalities. It's possible to have an intelligent conversation, to think and consider and weigh issues. It’s possible to understand what another person is saying, and perhaps be persuaded or persuade people on the other side. It's possible the change your mind or at least come to understand what is in another's mind.
An abusive ad hominem response is not “disagreeing” with someone, it’s being disagreeable, something else entirely. And starting an statement with a crack such as: “I've never been able to understand women . . . ”, well, that’s pathetic.
Some people have never learned to debate an issue without being abusive. When you ask them politely to back off, they get all haughty and even more abusive. Ad nauseum.