  The essential feature of atoms which does the most work in Gassendi's physics—and also generates the most difficulties—is their inherent weight, which gives them an intrinsic, natural tendency to move. Given this tendency, atomic rest is either provisionary or else an illusion. Atomic weight gives rise not only to a simple capacity for constant motion, but also to a range of more complex behaviors, enabling atoms to “…disentangle themselves, to free themselves, to leap away [prosiliendi, to spring out], to knock against other atoms, to turn them away [retundendi, to check], to move away from them, and similarly [they have] the capacity to take hold of each other, to attach themselves to each other, to join together, to bind each other fast…” Three other facets of atomic motion merit our attention.  First, it must be the general tendency of atoms to move in straight lines given that the atoms here do not feature the clinamen, or swerve (contrary to the Epicurean tradition, though perhaps as Epicurus himself would say). Second, Gassendi proposes that God endows atoms with a robust set of capacities for moving themselves to varying degrees—leading some commentators to see Gassendi as a vitalist or animist. Finally, Gassendi subscribes to a seamless compositionality of matter and scalar invariance regarding the nature and laws of motion, each of which lead him into murky waters. On the micro-level, he is committed to a constancy of motion that cannot be permanently arrested, whereas on the macro-level, he holds that a principle of inertia governs the motion and rest of all bodies.