But that's not the only theory about the function of sleep.

It is the only theory that appears to fit all the facts.

I still don't see how it was possible, but it's the only theory that makes sense.

For a long time this was the only theory about her origins.

Also he happens to have the only theory in town about the crashes.

Thus special relativity is the only theory which explains both experiments.

I've told you the only theory I can think of that could satisfy anybody.

True, it was the only theory which fitted all the facts.

The doctors cleared him of heart trouble, but the only theory they could come up with was that he had not been eating well.

The only theory to support this approach is the one stating that taxes reduce people's desire to work.