Once upon a time, it was weird to drive alone in your car with your lips moving.

In the dark days before Bluetooth technology, a jabbering jaw on a bouncing head meant a driver was singing along with the radio. But a moving mouth on a stationary noggin meant the driver was arguing with an invisible leprechaun about whether she should burn down the nearest Arby's.

Lucky for me, my most recent bout of behind-the-wheel babbling took place in an age when I just might have passed for sane. I was not. I was chanting over and over a single sentence — a perfect example I heard on the radio of someone opting not to use the subjunctive mood.

All I had to do was hold the precious example sentence in my head until I could get to my desk and jot it down. Then this column would practically write itself.

The strategy was working fine, right until I pulled into the parking lot at work and saw a Jaguar taking up two parking spaces, one of which should have been mine. That's when my gem of an example sentence was pushed out of my head by something that sounded more like dialogue from "Deadwood."

The sentence that slipped away was a perfect example of how you don't have to use the subjunctive if you don't want to, which in turn was a great segue to talk about the subjunctive in general. But now, in lieu of a good real-world example, here's a lame one I just made up: "It's crucial that he takes his medication."

One letter, the "s" at the end of "takes" renders that whole sentence not subjunctive. That doesn't make it wrong, mind you. Language authorities are careful never to say that the subjunctive is the only correct choice in these situations. It's just that people who pay attention consider the subjunctive the more proper choice.

So here's how to use it.

The term subjunctive mood applies to sentences that qualify as either "contrary to fact" — for example, a wish or a what-if — or a command, demand or statement of necessity. So in our example sentence, the words "it's crucial" make the whole sentence a statement of necessity.

In a present-tense sentence like this, you form the subjunctive by replacing the conjugated verb, in this case "takes," with what's called the base form of the verb, in this case "take." So "he takes" drops the "s" in "It's crucial that he take ..."

In some cases, the difference is undetectable because the conjugated verb just happens to be identical to the base form. Look at: I take, you take, he takes, she takes, it takes, we take, and they take. Only the third-person singular form ends in "s."

So had our sample sentence used the first-person singular "I" or the third-person plural "they," the verb would have been "take" no matter what. That is, "They take their medication" made subjunctive by adding "It's crucial that" wouldn't change: "It's crucial that they take ..."

But that's just in the present tense. In the past tense, the subjunctive really applies to just one verb: "was." The rule is simple: change "was" to "were." This comes up mostly in "if" statements and other hypotheticals.

So if you take, "I was a good student" and put "if" in front of it, you'd have a subjunctive mood situation and you'd change "was" to "were": If I were a good student. The same is true for wishes: I wish I were, not was, a good student.

Or perhaps a more accurate example would be: I wish I were better at remembering things I hear in the car.

JUNE CASAGRANDE is author of "It Was the Best of Sentences, It Was the Worst of Sentences." She can be reached at JuneTCN@aol.com.