changes successively its relation, its tendency, its correspondence, the position of its parts, either relatively to the different points of space, or to the different organs of the body which it puts in action: but to change its relation with space, with the organs to which it gives impulse, it follows of necessity that this spirit most have extent, solidity, consequently distinct parts: whenever a substance possesses these qualities, it is what we call matter, it can no longer be regarded as a simple pure being, in the sense attached to it by the moderns, or by theologians.
Thus it will be seen, that those who, to conquer insurmountable difficulties, have supposed in man an immaterial substance, distinguished from his body, have not thoroughly understood themselves; indeed they have done nothing more than imagined a negative quality, of which they cannot have any correct idea: matter alone is capable of acting on our senses; without this action nothing would be capable of making itself known to us. They have not seen that a being without extent is neither in a capacity to move itself, nor has the capability of communicating motion to the body; since such a being, having no parts, has not the faculty of changing its relation, or its distance, relatively to other bodies, nor of exciting motion in the human body, which is itself material. That which is called our soul moves itself with us; now motion is a property of matter—this soul gives impulse to the arm; the arm, moved by it, makes an impression, a blow, that follows the general law of motion: in this case, the force remaining the same, if the mass was two-fold, the blow should be double. This soul again evinces its materiality in the invincible obstacles it
