Contrary
to the popular use of the word in everyday language, a theory in science is something that models observed behaviour and is true, but not
absolutely so. E.g. The theories of special and general relativity. So a
theory isn't a postulation or idea which may or may not be true. E.g.
that there is water under the surface of some planet. Theories can be
updated to more accurately describe something. So for instance the laws
of motion don't work at velocities near the speed of light, so the
special theory of relativity caters for that scenario. Theorems unlike
theories however can be absolutely proved using axioms. E.g. the
triangle sum theorem which states that all the angles in a triangle add
up to 180 degrees.
