I should preface this question by saying that I am not familiar with Einstein's general relativity, so I am trying to understand the relationship between gravitational and inertial mass from a purely classical standpoint. Newton writes that the gravitational force exerted by an object is proportional to that object's inertial mass. As far as I know the only reliable way to define or measure mass is by measuring the acceleration caused by the application of a known force and quantifying this with respect to a reference mass. Thus inertial mass is defined as an object's ability to resist being accelerated or decelerated by some force. Applying this definition of mass to the law of universal gravitation, we find that the gravitational force associated with some object is proportional to that object's ability to resist being moved by a force. This seems like too straightforward a connection to be merely coincidental. My question then is this, how are we to understand the relationship between inertial mass and gravitational mass? Particularly, is it possible that an object gains its ability to resist being moved by a force (i.e. gains its inertial mass) by virtue of the fact that it is pulled by a contrary gravitational force towards surrounding objects? For example, suppose we place a ping pong ball and a brass ball in space and subject them each to an identical force -- we project each with a spring loaded plate. The ping pong ball is projected faster and farther than the brass ball. We want to say this is because the brass ball is more massive. But is it possible that all we are expressing in this statement is that, due to gravity, the brass ball is attracted to the spring loaded plate with a greater force than the ping pong ball, and is therefore endowed with a greater ability to resist the force of the spring?