From these hypotheses concerning the substance and local conjunction of our perceptions, we may pass to another, which is more intelligible than the former, and more important than the latter, viz. concerning the cause of our perceptions.  Matter and motion, it is commonly said in the schools, however varyed, are still matter and motion, and produce only a difference in the position and situation of objects.  Divide a body as often as you please, it is still body.  Place it in any figure, nothing ever results but figure, or the relation of parts.  Move it in any manner, you still find motion or a change of relation.  It is absurd to imagine, that motion in a circle, for instance, should be nothing but merely motion in a circle; while motion in another direction, as in an ellipse, should also be a passion or moral reflection:  That the shocking of two globular particles should become a sensation of pain, and that the meeting of two triangular ones should afford a pleasure.  Now as these different shocks, and variations, and mixtures are the only changes, of which matter is susceptible, and as these never afford us any idea of thought or perception, it is concluded to be impossible, that thought can ever be caused by matter.

Few have been able to withstand the seeming evidence of this argument; and yet nothing in the world is more easy than to refute it.  We need only reflect on what has been proved at large, that we are never sensible of any connexion betwixt causes and effects, and that it is only by our experience of their constant conjunction, we can arrive at any knowledge of this relation.  Now as all objects, which are not contrary, are susceptible of a constant conjunction, and as no real objects are contrary [Part iii.  Sect. 15.]; I have inferred from these principles, that to consider the matter A priori, any thing may produce any thing, and that we shall never discover a reason, why any object may or may not be the cause of any other, however great, or however little the resemblance may be betwixt them.  This evidently destroys the precedent reasoning concerning the cause of thought or perception.  For though there appear no manner of connexion betwixt motion or thought, the case is the same with all other causes and effects.  Place one body of a pound weight on one end of a lever, and another body of the same weight on another end; you will never find in these bodies any principle of motion dependent on their distances from the center, more than of thought and perception.  If you pretend, therefore, to prove a priori, that such a position of bodies can never cause thought; because turn it which way you will, it is nothing but a position of bodies; you must by the same course of reasoning conclude, that it can never produce motion; since there is no more apparent connexion in the one case than in the other.  But as this latter conclusion is contrary to evident experience, and as it is possible we may