 This is a passage rich with meaning. Leibniz clearly insisted that vortices, or some physical object or fluid, must be in contact with the planetary orbits if we are to explain why they deviate from the tangents along the orbital paths when circling the sun. Newton’s reply is that giant swirling fluids in the heavens would actually disturb the regular orbital paths and the paths of comets through the solar system. That reply might be thought of as empirical in character, for it depends on observational data regarding the actual paths of the heavenly bodies. But Leibinz’s perspective is obviously not merely empirical in character: he does not postulate vortices (or anything akin to them) on observational grounds; he infers their existence because he thinks we know (perhaps we can add, we know a priori) that physical bodies such as comets or planets can deviate from a rectilinear path—they can accelerate—only if some other physical item impacts upon them. Newton has a reply to that kind of view as well: he insists that the phenomena of the motion of the heavenly bodies “follows” solely from gravity itself—an impressed force, as we have seen, and therefore an “action”—in accordance with the laws of motion and the law of universal gravitation. Since gravity is an action—clearly, a causal notion—it seems clear that Newton’s answer to Leibniz’s idea that vortices cause the planetary orbits is that gravity itself causes them. It is not much of a leap to conclude, in turn, that this reply commits Newton to the idea that bodies involved in gravitational interactions, such as the sun and the earth, act at a distance on one another through the force of gravity. It is not hard to divine why Leibniz (and Huygens) would have concluded that Newton had relinquished any commitment to the norms of the mechanical philosophy.