Nevertheless, to justify such monstrous opinions, they assert that ideas are only the objects of thought. But according to the last analysis, these ideas can only reach man from exterior objects, which in giving impulse to his senses modify his brain; or from the material beings contained within the interior of his machine, who make some parts of his body experience those sensations which he perceives, which furnish him with ideas, which he relates, faithfully or otherwise, to the cause that moves him. Each idea is an effect, but however difficult it may be to recur to the cause, can we possibly suppose it is not ascribable to a cause? If we can only form ideas of material substances, how can we suppose the cause of our ideas can possibly be immaterial? To pretend that man without the aid of exterior objects, without the intervention of his senses, is competent to form ideas of the universe, is to assert, that a blind man is in a capacity to form a true idea of a picture, that represents some fact of which he has never heard any one speak. It is very easy to perceive the source of those errors, into which men, otherwise extremely profound and very enlightened have fallen, when they have been desirous to speak of the soul: to describe its operations. Obliged either by their own prejudices, or by the fear of combatting the opinions of some imperious theologian, they have become the advocates of the principle, that the soul was a pure spirit: an immaterial substance; of an essence directly different from that of the body; from every thing we behold: this granted, they have been incompetent to conceive how material objects could operate, in what manner gross and corporeal organs were enabled to act on a substance, that had no kind of analogy with them; how they were in a capacity to modify it by conveying its ideas; in the impossibility of explaining this phenomenon, at the same time perceiving that the soul had ideas, they concluded that it must draw them from itself, and not from those beings, which according to their own hypothesis, were incapable of acting on it, or rather, of which they could not conceive the manner of action; they therefore imagined that all the modifications, all the actions of this soul, sprung from its own peculiar energy, were imprinted on it from its first formation, by the Author of Nature: that these did not in any manner depend upon the beings of which we have a knowledge, or which act upon it, by the gross means of our senses.