I do not think Newton ever used the pushing force concept... especially later after formulating his laws of motion and inertia..
There is some interesting reading on Wikipedia (
http://en.wikipedia.org/wiki/Philoso...ia_Mathematica)
about his Principia. Bthw, he was not the only person at the time who was thinking about why planets orbit the Sun and inverse square law of gravitational attraction, which must be adopted to explain the measured motions.