It must be acknowledged that highly curious as this preliminary disquisition is, it is not only unnecessary to the main argument, but leaves the definition of matter open to the question whether there be any substratum or subject in which the essential properties or powers of attracting and repelling inhere. That these powers really belong to matter, whatever else matter may be, is evident from the reflection of light, previous to contact with the reflecting substance and its inflection afterward from the electric spark, visible along a suspended chain, from the phenomena of the metallic pyrometers, from the rain drop on a cabbage leaf, &c. And that matter is permeable, at least to light, is sufficiently evident from every case of tranparency. Still however it cannot consist of properties alone; a property must be the property of something. But the proper and direct train of argument in favour of materialism is, that every phenomenon from which the notion of a soul is deduced, is resolveable into some affection of the brain, perceived. That all thought, reflection, choice, judgment, memory, the passions and affections, &c. consist only of ideas or sensations,(i. e. motions within that organ) perceived at the time. Though, judgment, memory, being words, denoting different kinds of internal perceptions, relating only to, and consisting of, ideas and sensations.[67] That sensations and ideas themselves, arise only in consequence of the impressions of external objects on our senses, which impressions are liable to be recalled afterward by the recurrence of others with which they were originally associated, agreeably to the necessary and inevitable law of the animal system. That this is evident in as much as there can be no ideas peculiar to any of the senses where there is a want of the necessary bodily organ, as of hearing, sight, &c. inasmuch as all these ideas commence with the body, grow with its growth, and decrease with its decline. That they can be suspended, altered, destroyed, by artificial means, by accident, by disease. That all these properties of mind, viz. thought, judgment, memory, passions, and affections, are as evident in brutes as in men; and though the degree be different, it is always accompanied with a proportionate difference of organization. That perception is clearly the result of organization, being always found with it, and never without it: as clearly so in other animals as in the human species; and probably in vegetables though in a still lower degree.[68] That as all the common phenomena of mind, can be accounted for from the known facts of organized matter without the souls, and as none of them can possibly be attributed to the soul without the body, there is no necessity to recur to any gratuitous theory in addition to the visible corporeal frame. That the doctrine of the soul originated in ignorance, and has been supported by imposture; that it involves gross contradictions and insuperable difficulties, and is no more countenanced by true religion than by true philosophy.
[67] A Sensation is an impression made by some external object on the Senses; the motion thus excited is propagated along the appropriate nerve, until it reaches the Sensory in the Brain, and it is there and there only, felt or perceived.
An Idea, is a motion in the Brain, excited there either by the laws of association to which that organ is subject, or by some accidental state of the system in general, or that organ in particular, without the intervention of an impression on the Senses ab extra as the cause of it. Such a motion being similar to a sensation formerly excited, and being also felt or perceived is the correspondent Idea.
[68] Dr. Percival, Dr. Bell in the Manchester Transactions, and Dr. Watson in the last volume of his essays, have made this opinion highly probable. Many additional observations are to be found in Dr. Darwin’s works. I consider it as a theory established.
All this has been shewn with great force of argument and ingenuity by Dr. Priestley in these disquisitions, to which it may safely be affirmed nothing like a satisfactory answer has yet been given, or is ever likely to be given. True metaphysics, like every other branch of philosophy can only be founded on an accurate observation of facts, and as these become gradually substituted for mere names, our real knowledge will improve. It is to physiology perhaps that the question of the materiality of the human soul, and even that of liberty and necessity will owe the compleatest elucidation. Until medical writers brought into view the facts relating to animal life, the metaphysical disquisitions on these subjects were involved in an endless confusion of words without precise meaning, and almost always including in their definition a petitio principii. Indeed we are not yet fully apprized either in Law, Physic or Divinity any more than in Metaphysics, that the species intelligibiles of the old schoolmen, and the whole class of abstract ideas of the new schoolmen with Locke at their head, are not things, but names. They are not even either sensations or ideas; they are words, convenient indeed for classification, and used artificially like the signs of Algebra, but they have no archetype. This is a subject which will probably be better understood ere long by the labours of Mr. Horne Tooke.
Dr. Priestley therefore considered the question of a future state, as now rested on the basis which to a christian is or ought to be perfectly satisfactory; on the promises and declarations of our Saviour, exemplified by his own resurrection from the dead. Indeed the circumstances of the whole question of futurity depending on the truth of the christian scriptures and on them alone, is calculated to give them a peculiar and inestimable value in the eyes of those who look forward with anxious hope[69] to a continued and more perfect state of existence after death. Nor is it of any consequence to the christian, that the manner how this will be effected is not plainly revealed; for it is sufficient that the Being who first gave animation to the human frame, will at his own time and in his own manner for the wisest and best of purposes, again exert the same act of almighty power in favour of the human race, and in fulfillment of his promise through Jesus Christ. Such at least was the view of the subject habitually entertained by our author.
[69] There are some persons who do not seem to entertain this anxious hope. Mr. Gray the poet seems an instance, from the following passage in his ode Barbaras Ædes aditure mecum (Letters V. 2 p. 44) though I do not recollect that the sentiment has been noticed before.
Oh ego felix, vice si (nec unquam
Surgerem rursus) simili cadentem
Parca me lenis sineret quieto