theory of gravitation
theory of gravity
gravitational theory
Newton's theory of gravitation

It is often considered the work that finally brought about general acceptance of Newton's optical and gravitational theories.

Newton's gravitational theory gave an example, by restricting itself to the pure mechanics of gravitation.

In his later years he worked on gravitational theory.

Fierz also worked on gravitational theory but published only one paper on the subject.

Many of his ingenious hunches were later realized in Einstein's gravitational theory.

The programme implicit in Newton's gravitational theory gave strong heuristic guidance.

Then the Cavendish extrapolation on gravitational theory produced negative transformations.

Brown's objective had been to produce an accurate ephemeris of the Moon, based purely on gravitational theory.

Maybe we should borrow from gravitational theory, call it a new kind of event horizon?

Your teacher could counter that gravitational theory is wrong; magic holds us to the earth.