Theory and practice should go hand in hand.

In theory it is possible, but in practice it is very difficult.

We have to consider the problem in the light of cultural differences.

Please explain in detail.

Everyone will accept that idea in principle.

Bear in mind what he said.

He was in time for the appointment.

All of the rules must be in line with company policy.

Mother was busily cooking; in the meantime, I was just watching TV.

A more plausible proposal is the one Leech presented in conjunction with Emmet's theory.