Political correctness and common sense have something in common.

No, it isn’t that opposing political correctness is just common sense. What they share is argument by assertion. Once you say something is just common sense (or, as political speechwriters are wont to do these days, to apply the adjective “commonsense” to whatever preposterous proposition their employer is promoting that day) … once you use the phrase you’ve eliminated the need for evidence or logic. Like placing “Q.E.D.” at the end of a geometric proof, you have no more ‘splainin’ to do.

Complaining about political correctness is like that too. Make the complaint and there’s no room for further discussion.

And yet, there’s little about politically correctness that’s cut and dried, except, perhaps, for both extremes of the linguistic spectrum. For example, very few of us favor casual use of racial or ethnic slurs. But how about:

• Quite a few years ago now, David Howard, then head of the Washington DC Office of Public Advocate, used the word “niggardly” in a conversation about funding.

It’s a perfectly fine word, with a precise, appropriate meaning and a clean and wholesome etymology. Nonetheless, Howard was forced to resign for using it because he should have known he might be misunderstood.

My guess: The people who criticized him were a bunch of Homo sapiens.

• Huckleberry Finn. This was Mark Twain’s magnum opus against racism. In it, Nigger Jim (you have no idea how hard it was for me to even type his name) is a more sympathetic character than most of the upstanding white citizens in the book.

And in one of the truly brilliant bits in the history of satire, Huck Finn and Tom Sawyer wrestle with their consciences, and finally decide to do the morally wrong thing. They hide their friend from those who would return him to slavery, even though they knew they’d surely go to Hell for it.

Every so often some well-intentioned souls want to ban this, one of the most important works in the history of American race relations, from school bookshelves, mostly because of its authentic vernacular. One suspects they’re ignorant of earlier attempts to ban the book … yes, that’s right, by those who considered it anti-Southern and who complained that it encouraged sympathy for escaped slaves.

• Blazing Saddles, one of the funniest movies ever, with a powerful message about bigotry, too. Mel Brooks has his cast use the n-word and other racial and ethnic slurs so often and so casually audiences eventually become desensitized to the language.

It’s hard to see how Brooks could have written the script any other way, and the language is, to my way of thinking at least, pitch-perfect for its era and purpose. If you disagree, try re-writing the movie’s punchline in more sensitive language — the line where Rock Ridge’s mayor, called on to be fully inclusive, declines, saying, “We’ll take the Niggers and the Chinks, but we don’t want the Irish!”

(Plot spoiler: Cleavon Little persuades the townsfolk to accept the Irish, too.)

And now, to blur things even more, we have micro-aggression — defined as speech that falls short of overt bigotry but that still subtly demeans or stereotypes members of an already-marginalized group.

I have no doubt micro-aggression is real. For example I recall squirming when a saleswoman told my wife and me a dining room table we liked was made of “Coolie wood,” entirely oblivious to what she was saying.

For that matter I cringe when I hear people tossing off demeaning workplace words and phrases like geek, bean-counter, and pointy-haired boss. None of these is likely to cause an IT professional, accountant, or business manager to burst into tears. Language does shape attitudes, though. And stereotypes guide and reinforce expectations.

On the other hand, there’s no easy line that separates the hyenas’ ghetto-speak in Disney’s The Lion King from the Lucky Charms leprechaun’s stage Irish.

So let’s just lose the phrase “politically correct” altogether. It adds nothing and obscures lots. We don’t need to stamp anything out. We do need to find the line that separates patently offensive speech from listening with paper-thin skins. This sure would be handy, because avoiding offense shouldn’t lead us all to just give up and sew our collective lips together.

What it won’t be is easy. It isn’t, that is, just a matter of … dare I say it? … common sense.