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.

’VI.  Caesar’s soul is a being to which unity belongs in a strict sense.  The faculty of producing thoughts is a property of its nature (so M. Leibniz), which it has received from God, both as to possession and exercise.  If the first thought it produces is a sense of pleasure, there is no reason why the second should not likewise be a sense of pleasure; for when the total cause of an effect remains the same, the effect cannot be altered.  Now this soul, at the second moment of its existence, does not receive a new faculty of thinking; it only preserves the faculty it had at the first moment, and it is as independent of the concourse of any other cause at the second [43] moment as it was at the first.  It must therefore produce again at the second moment the same thought it had produced just before.  If it be objected that it ought to be in a state of change, and that it would not be in such a state, in the case that I have supposed; I answer that its change will be like the change of the atom; for an atom which continually moves in the same line acquires a new situation at every moment, but it is like the preceding situation.  A soul may therefore continue in its state of change, if it does but produce a new thought like the preceding.

’But suppose it to be not confined within such narrow bounds; it must be granted at least that its going from one thought to another implies some reason of affinity.  If I suppose that in a certain moment the soul of Caesar sees a tree with leaves and blossoms, I can conceive that it does immediately desire to see one that has only leaves, and then one that has only blossoms, and that it will thus successively produce several images arising from one another; but one cannot conceive the odd change of thoughts, which have no affinity with, but are even contrary to, one another, and which are so common in men’s souls.  One cannot apprehend how God could place in the soul of Julius Caesar the principle of what I am going to say.  He was without doubt pricked with a pin more than once, when he was sucking; and therefore according to M. Leibniz’s hypothesis which I am here considering, his soul must have produced in itself a sense of pain immediately after the pleasant sensations of the sweetness of the milk, which it had enjoyed for the space of two or three minutes.  By what springs was it determined to interrupt its pleasures and to give itself all of a sudden a sense of pain, without receiving any intimation of preparing itself to change, and without any new alteration in its substance?  If you run over the life of that Roman emperor, every page will afford you matter for a stronger objection than this is.