You know how long and hard we've looked for a general theory.

It took some time for the current theory to be worked out.

There is much to be said for such a theory.

Sometimes in return for his theories she gave out some fact of her own life.

This study is central for the theory of natural capital.

The findings, they said, provide clear evidence for the first theory.

Way back at the beginning of his career as a director he admitted having no use for theory.

He indicates the need for, but does not provide, a theory of history.

India is also where he turns for a theory of history.

There is something to be said for the theory of suicide which you have put forward.