'Let us return to the soul of Julius Caesar, and call it an immaterial automaton (M. Leibniz's own phrase), and compare it with an atom of Epicurus; I mean an atom surrounded with a vacuum on all sides, and which will never meet any other atom. This is a very just comparison: for this atom, on the one hand, has a natural power of moving itself and exerts it without any assistance, and without being retarded or hindered by anything: and, on the other hand, the soul of Caesar is a spirit which has received the faculty of producing thoughts, and exerts it without the influence [42] of any other spirit or of any body. It is neither assisted nor thwarted by anything whatsoever. If you consult the common notions and the ideas of order, you will find that this atom can never stop, and that having been in motion in the foregoing moment, it will continue in it at the present moment and in all the moments that shall follow, and that it will always move in the same manner. This is the consequence of an axiom approved by M. Leibniz: _since a thing does always remain in the same state wherein it happens to be, unless it receives some alteration from some other thing ... we conclude_, says he, _not only that a body which is at rest will always be at rest, but that a body in motion will always keep that motion or change, that is, the same swiftness and the same direction, unless something happens to hinder it_. (M. Leibniz, ibid.) 'Everyone clearly sees that this atom, whether it moves by an innate power, as Democritus and Epicurus would have it, or by a power received from the Creator, will always move in the same line equally and after a uniform manner, without ever turning or going back. Epicurus was laughed at, when he invented the motion of declination; it was a needless supposition, which he wanted in order to get out of the labyrinth of a fatal necessity; and he could give no reason for this new part of his system. It was inconsistent with the clearest notions of our minds: for it is evident that an atom which describes a straight line for the space of two days cannot turn away at the beginning of a third, unless it meets with some obstacle, or has a mind all of a sudden to go out of its road, or contains some spring which begins to play at that very moment. The first of these reasons cannot be admitted in a vacuum. The second is impossible, since an atom has not the faculty of thinking. And the third is likewise impossible in a corpuscle that is a perfect unity. I must make some use of all this.