Monday, November 17, 2008

used to have to must

Okay, I'm going to do a couple of English grammary things that have come up, for those (she? are there more than one?) who like that kind of thing.

First up, which is the correct negative for "used to": "didn't used to" or "didn't use to"? People get very confused but the answer is simple, and reasonably easy to remember.

"Use to" is exactly like "want to" or "like to", except that we do not use it in the present tense any more. (You can find it in Shakespeare, I believe.)

We say, "I liked to go to the football" and "I didn't like to go the football", and we say, "I used to go to the football" and "I didn't use to go to the football". Easy.

Second, this came up in a course I'm editing: what difference in meaning is there between "have to" and "must"? The poor soul who wrote the course got in a muddle trying to capture it, because the difference is thin and not very important, although it does exist.

It's fairly simple. "Have to" has a flavour -- and no more than a flavour, really -- of compulsion from the outside (or often an abstract compulsion), while "must" can have a flavour of choice, of self-imposed compulsion (or even a more concrete compulsion).

What I mean is that "I have to go" is what you tend to say when you need to catch a train; "I must go" is what you tend to say when you really want to go or you have set a time to go. Don't get me wrong; they are quite interchangeable, and you would not be wrong to say either in either situation, but the hint of a difference is there.

You'd notice though that if you had a hundred instances where you could choose, you might perhaps in 80 choose "have to" in sentences like "you have to/must watch Quantum of Solace, it's really good". Here, the compulsion is abstract: no one is forcing you to watch it, but you must watch it (if you like films, if you want to be able to join in at the watercooler, if you don't want me to mock you, and so on). Conversely, you might more often choose "must" in sentences like "you must park between the lines".

Note that you can only use "must" in the negative. I don't know why that is, but it's tempting to feel that negatives are not as abstract as positives. I'll have to think some about that, because it feels true but I don't know why.