As I watched a small slug inch its way across one of my paving stones this morning, something lurched out of the shadows in the back of my memory. It wasn’t something that I know happened, or a specific incident that I can relate. There was no beginning, so there could be no middle and certainly no end. But it was as real as anything that originates in the mind and stays there.

The only detail that penetrated the mist was the back yard of my old place next door, where I lived for all of four months nearly five years ago. I saw a slug there, too, and then it was gone. I can’t say for sure that it ever happened, but it might as well have, because the memory of it was as real as if it had. And then it was gone, like the memory of a dream.

It made me ponder what mysteries are inside my head, ready to reveal themselves to me under the right provocation. And it made me wonder, for a moment, if I could stimulate these mysteries consciously. Then I remembered the nature of this kind of memory, fleeting and insubstantial.

I know what you’re thinking. (That’s a different kind of phenomenon altogether, though.) You’re thinking, “Déjà vu.” And you’re right, in a sense. But I wonder if it’s not also a result of having lived this many years. Maybe after so many decades on this planet, a person accumulates so many sensory images that almost anything real can trigger almost anything psychic at almost any time.

So I’ve decided that déjà vu is in a way the realization that there is a finite number of experiences a person can gather in a lifetime, although there might be infinitely many permutations of those experiences. You can’t see or do something that hasn’t been seen or done before. And if you’ve lived long enough, you’re probably the person who saw or did it.

The exception, of course, is baseball. It’s an accepted maxim by aficionados that every time you watch a baseball game you’ll see something you’ve never seen before. I’ve seen enough games to know that this is true.