The more man reflects, the more he will be convinced that the soul, very far from being distinguished from the body, is only the body itself, considered relatively to some of its functions, or to some of the modes of existing or acting, of which it is susceptible whilst it enjoys life. Thus, the soul is man, considered relatively to the faculty he has of feeling, of thinking, of acting in a mode resulting from his peculiar nature; that is to say, from his properties, from his particular organization: from the modifications, whether durable or transitory, which the beings who act upon him cause his machine to undergo.
Those who have distinguished the soul from the body, appear only to have distinguished their brain from themselves. Indeed, the brain is the common center, where all the nerves, distributed through every part of the body, meet and blend themselves: it is by the aid of this interior organ that all those operations are performed which are attributed to the soul: it is the impulse, or the motion, communicated to the nerve, which modifies the brain: in consequence, it re-acts, or gives play to the bodily organs; or rather it acts upon itself, and becomes capable of producing within itself a great variety of motion, which has been designated intellectual faculties.
From this it may be seen that some philosophers have been desirous to make a spiritual substance of the brain. It is evidently nothing but ignorance that has given birth to and accredited this system, which embraces so little, either of the natural or the rational. It is from not having studied himself, that man has supposed he was compounded with an agent, essentially different from his body: in examining this body, he will find that it is quite useless to recur to hypothesis for the explanation of the various phenomena it presents to his contemplation; that hypothesis can do nothing more than lead him out of the right road to the information after which he seeks. What obscures this question, arises from this, that man cannot see himself: indeed, for this purpose, that would be requisite which is impossible; namely, that he could he at one and the same moment both within and without himself: he may be compared to an Eolian harp, that issues sounds of itself, and should demand what it is that causes it to give them forth? It does not perceive that the sensitive quality of its chords causes the air to brace them; that being so braced, it is rendered sonorous by every gust of wind with which it happens to come in contact.
When a theologian, obstinately bent on admitting into man two substances essentially different, is asked why he multiplies beings without necessity? he will reply, because "thought cannot be a property of matter." If, then, it be enquired of him, cannot God give to matter the faculty of thought? he will answer, "no! seeing that God cannot do impossible things!" According to his principles, it is as impossible that spirit or thought can produce matter, as it is impossible that matter can produce spirit or thought: it might, therefore, be concluded against him, that the world was not made by a spirit, any more than a spirit was made by the world. But in this case, does not the theologian, according to his own assertion, acknowledge himself to be the true atheist? Does he not, in fact, circumscribe the attributes of the Deity, and deny his power, to suit his own purpose? Yet these men demand implicit belief in doctrines, which they are obliged to maintain by the most contradictory assertions.
The more experience we collect, the more we shall be convinced that the word spirit, in its present received usage, conveys no one sense that is tangible, either to ourselves or to those that invented it; consequently cannot be of the least use, either in physics or morals. What modern metaphysicians believe and understand by the word, is nothing more than an occult power, imagined to explain occult qualities and actions, but which, in fact, explains nothing. Savage nations admit of spirits, to account to themselves for those effects, which to them appear marvellous, as long as their ignorance knows not the cause to which they ought to be attributed. In attributing to spirits the phenomena of Nature, as well as those of the human body, do we, in fact, do any thing more than reason like savages? Man has filled Nature with spirits, because he has almost always been ignorant of the true causes of those effects by which he was astonished. Not being acquainted with the powers of Nature, he has supposed her to be animated by a great spirit: not understanding the energy of the human frame, he has in like manner conjectured it to be animated by a minor spirit: from this it would appear, that whenever he wished to indicate the unknown cause of a phenomena, he knew not how to explain in a natural manner, he had recourse to the word spirit. In short, spirit was a term by which he solved all his doubts, and cleared up his ignorance to himself. It was according to these principles that when the AMERICANS first beheld the terrible effects of gunpowder, they ascribed the cause to wrathful spirits, to their enraged divinities: it was by adopting these principles, that our ancestors believed in a plurality of gods, in ghosts, in genii, &c. Pursuing the same track, we ought to attribute to spirits gravitation, electricity, magnetism, &c. &c. It is somewhat singular, that priests have in all ages so strenuously upheld those systems which time has exploded; that they have appeared to be either the most crafty or the most ignorant of men. Where are now the priests of Apollo, of Juno, of the Sun, and a thousand others? Yet these are the men, who in all times have persecuted those who have been the first to give natural explanations of the phenomena of Nature, as witness ANAXAGORAS, ARISTOTLE, GALLILEO, DESCARTES, &c. &c.
CHAP. VIII.
The Intellectual Faculties derived from the Faculty of Feeling.
To convince ourselves that the faculties called intellectual, are only certain modes of existence, or determinate manners of acting, which result from the peculiar organization of the body, we have only to analyze them; we shall then see that all the operations which are attributed to the soul, are nothing more than certain modifications of the body; of which a substance that is without extent, that has no parts, that is immaterial, is not susceptible.