I'm no physicist by any stretch of the imagination, but one concept has always fascinated me: I believe it was Einstein who postulated that time and space are interrelated, that in some ways time IS space, and space IS time. And that came to mind when I thought about President Bush's speech the other day, and the calls for the "exit strategy" from Iraq.

There are two ways of measuring the completion of a task: by time, and by action. A lot of Democrats wish to define the end of the Iraq war by a calendar -- so many troops out by such a time, more by a later date, complete withdrawal by a third, and the like.

But I don't think this is one of those tasks that can be measured that way. I think that President Bush intends it to be one of the latter -- to be determined by events, not time -- and I think he's right.

Some events are better defined that way. For instance, one's date of birth is not determined by simply calculating the date of conception and adding in nine months. That's how long it takes most of the time, but it's an average. Some take longer, some come sooner.

In school, we've tried the calendar approach for progression. Under the label of "social promotion," students are advanced in grade to keep up with their peer groups, regardless of their achievements. It was an unmitigated disaster, and nearly every school system that I've ever heard of trying it ended up abandoning it as ultimately destructive for the students.

Over two years ago, Steven Den Beste outlined how he saw the war in Iraq had developed, and projected what it would take to win it. Over two years later, it still holds strong. We've reached Section VIII of his outline, and so far he's got a record for accuracy that would put a shiver of fear down Nostradus' back.

No, it's not going perfectly. But a hell of a lot of good has been achieved, and more and more is happening all the time -- listen to what the soldiers on the ground are saying, and you can hear it.

The only advantage a calendar-based approach is to tell the enemy just how long they have to hang on until we leave and let them win by default. And I don't think that is such a great idea.