  Newton explicitly rejected the idea that gravitation, or any other force, be essential to matter. But the major point of mechanical atomism had been to admit as properties of atoms only those that they must, essentially, have as pieces of matter. It was in this way that they had endeavoured to avoid introducing Aristotelian forms and qualities, which they regarded as incomprehensible from an ontological point of view. The introduction of forces as irreducible entities flew in the face of the major aim of the mechanical philosophers for clarity and intelligibility on ontological matters. Newton was unable to fashion an unambiguous view on the ontological status of gravity, a force manifest at the level of observation and experiment, let alone forces operative at the atomic level. It is true that, in the case of gravity, Newton had a plausible pragmatic response. He argued that, whatever the underlying status of the force of gravity might be, he had given a precise specification of that force with his law of gravitation and had employed the force to explain a range of phenomena at the astronomical and terrestrial level, explanations that had been confirmed by observation and experiment. But not even a pragmatic justification such as this could be offered for forces at the atomic level.