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Nature of the mechanism -- Its classes, material and intellectual. -- Material system, or of vibrations. -- The intellectual system most probable -- From the consideration that thought would otherwise be a superfluity -- From the established principles of reasoning from effects to causes. -- Objections refuted. -- Thoughts which produce animal motion may be -- 1. Involuntary. All animal motions were first involuntary. -- 2. Unattended with consciousness. -- The mind cannot have more than one thought at any one time -- Objection to this assertion from the case of complex ideas -- From various mental operations -- As comparison -- Apprehension -- Rapidity of the succession of ideas. -- Application -- Duration measured by consciousness. -- 3. A distinct thought to each motion may be unnecessary. -- Apparent from the complexity of sensible impressions. -- The mind always thinks. -- Conclusion. -- The theory applied to the phenomenon of walking -- To the circulation of the blood. -- Of motion in general. -- Of dreams.{318} The doctrine of necessity being admitted, it follows that the theory of the human mind is properly, like the theories of every other series of events with which we are acquainted, {319} a system of mechanism; understanding by mechanism nothing more than a regular connexion of phenomena without any uncertainty of event, so that every incident requires a specific cause, and could be no otherwise in any respect than as the cause determined it to be.
But there are two sorts of mechanism capable of being applied to the solution of this case, one which has for its medium only matter and motion, and he other which has for its medium thought. Which of these is to be regarded the most probable?
According to the first we may conceive the human body to be so constituted as to be susceptible of vibrations, in the same manner as the strings of a musical instrument are susceptible of vibrations. These vibrations, having begun upon the surface of the body are conveyed to the brain; and, in a manner that is equally the result of construction, produce a second set of vibrations beginning in the brain, and conveyed to the different organs or members of the body. Thus it may be supposed, that a piece of iron considerably heated is applied to the body of an infant, and that the report of this uneasiness, or irritation and separation of parts being conveyed to the brain, vents itself again in a shrill and piercing cry. It is in this manner that we are apt to imagine certain convulsive and spasmodic affections to take place in the body. The case, as here described. is similar to that of the bag of a pair of bagpipes, which, being {320} pressed in a certain manner, utters a groan, without any thing more being necessary to account for this phenomenon, than the known laws of matter and motion. Let us add to these vibrations a system of associations to be carried on by traces to be made upon the medullary substance of the brain, by means of which past and present impressions are connected according to certain laws, as the trace happen to approach or run into each other; and we have then a complete scheme for accounting in a certain way for all the phenomena of human action. It is to be observed, that, according to this system, mind or perception is altogether unnecessary to explain the appearances. It might for other reasons be desirable or wise, to introduce a thinking substance or a power of perception as a spectator of the process. But the percipient power is altogether neutral, having no concern either as a medium or otherwise in producing the events1.
The second system, which represents thought as the medium {320} of operation is not less a system of mechanism, according to the doctrine of necessity, than the other, but it is a mechanism of a totally different kind.
There are various reasons calculated to persuade us that this last hypothesis is the most profitable. No inconsiderable argument may be derived from the singular and more important nature of that property of human beings, which we term thought; which it is surely somewhat violent to strike out of our system as a mere superfluity.
A second reason still more decisive than the former, arises from the constancy with which thought in innumerable instances accompanies the functions of this mechanism. Now this constancy of conjunction has been shewn to be the only ground we have in any imaginable subject for inferring necessary connexion, or that species of relation which exists between cause and effect. We cannot therefore reject the principle which supposes thought to have an efficient share in the mechanism of man, but upon grounds that would vitiate all our reasonings from effects to causes.
It may be objected, 'that, though this contiguity of event argues necessary connexion, yet the connexion may be exactly the reverse of what is here stated, motion being in all instances the cause, and thought never any thing more than an effect.' But this is contrary to every thing we know of the system of {322} the universe, in which each event appears to be alternately both the one and the other, nothing terminating in itself but every thing leading on to an endless chain of consequences.
It would be equally vain to object, 'that we are unable to conceive how thought can have any tendency to produce motion in the animal,' since it has just appeared that this ignorance is by no means peculiar to the subject before us. We are universally unable to perceive the ground of necessary connexion.
It being then sufficiently clear that there are cogent reasons to persuade us that thought is the medium through which the motions of the animal system are generally carried on, let us proceed to consider what is the nature of those thoughts by which the limbs and organs of our body are set in motion. It will then probably be found, that the difficulties which have clogged the intellectual hypothesis, are principally founded in erroneous notions derived from the system of liberty; as if there were any essential difference between those thoughts which are the medium of generating motion, and thoughts in general.
First, thought may be the source of animal motion, without partaking in any degree of volition or design. It is certain that there is a great variety of motions in the animal system, which are in every view of the subject involuntary. Such for example, are the cries of an infant, when it is first impressed {323} with the sensation of pain. Such must be all those motions which flowed from sensation previous to experience. Volition implies that something which is the subject of volition, is regarded as desirable; but we cannot desire any thing, till we have an idea corresponding to the term futurity. Volition implies intentions, or design; but we cannot design any thing, till we have the expectation that the existence of that thing is in some way connected with the means employed to produce it. An infant, when he has observed that a voice exciting compassion is the result of certain previous emotions, may have the idea of that voice predominant in his mind during the train of emotions that produce it. But this could not have been the case the first time it was uttered. In the first motions of the animal system, nothing of any sort could possibly be foreseen, and therefore nothing of any sort could be intended. Yet in the very instances here produced the motions have sensation or thought for their constant concomitant; and therefore all the arguments, which have been already alledged, remain in force to prove that thought is the medium of their production.
Nor will this appear very extraordinary, if we consider the nature of volition itself. In volition, if the doctrine of necessity be true, the mind is altogether passive. Two ideas present themselves as in some way connected with each other; and a perception of preferableness necessarily follows. An object having certain desirable qualities, is perceived to be within my reach; {324} and my hand is necessarily stretched out with an intention to obtain it. If a perception of preferableness and a perception of desirableness irresistibly lead to an animal motion, why may not the mere perception of pain? All that the adversary of automatism is concerned to maintain is, that thought is an essential link in the chain; and that, the moment it is taken away, the links that were before it have no longer any tendency to produce motion in the links that were after it. It is possible, that, as a numerous class of motions have their constant origin in thought, so there may be thoughts altogether unattended with motion.
Here it may be proper to observe, that, from the principles already delivered, it follows that all the original motions of the animal system are involuntary. In proportion however as we obtain experience, they are successively made the subjects of reflection and foresight; and of consequence become many of them the themes of intention and design, that is, become voluntary. We shall presently have occasion to suspect that motions, which were at first involuntary, and afterwards by experience and association are made voluntary, may in the process of intellectual operation be made involuntary again. -- But to proceed.
Secondly, thought may be the source of animal motion, and yet be unattended with consciousness. This is undoubtedly a distinction of considerable refinement, depending upon the precise {325} meaning of words; and, if any person should choose to express himself differently on the subject, it would be useless obstinately to dispute that difference with him. By the consciousness which accompanies any thought there seems to be something implied distinct from the thought itself. Consciousness is a sort of supplementary reflection, by which the mind not only has the thought, but adverts to its own situation and observes that it has it. Consciousness therefore, however nice the distinction, seems to be a second thought.
In order to ascertain whether every thought be attended with consciousness, it may be proper to consider whether the mind can ever have more than one thought at any one time. Now this seems altogether contrary to the very nature of mind. My present thought is that to which my present attention is yielded; but I cannot attend to several things at once. This assertion appears to be the nature of an intuitive axiom; and experience is perpetually reminding us of its truth. In comparing two objects we frequently endeavour as it were to drag them together in the mind, but we seem to be obliged to pass successively from the one to the other.
But this principle, though apparently supported both by reason and experience, is not unattended with difficulties. The first is that which arises from the case of complex ideas. This will best be apprehended if we examine it as relates to visible objects. {326} 'Let us suppose that I am at present employed in the act of reading. I appear to take in whole words and indeed clusters of words by a single act of the mind. But let it be granted for a moment that I see each letter successively. Yet each letter is made up of parts: the letter D for example of a right line and a curve, and each of these lines of the successive addition of fluxion of points. If I consider the line as a whole, yet its extension is one thing, and its terminations another. I could not see the letter if the black line that describes it and the white surface which bounds it were not each of them in the view of my organ. There must therefore, as it should seem, upon the hypothesis above stated, be an infinite succession of ideas in the mind, before it could apprehend the simplest objects with which we are conversant. But we have no feeling of any such thing, but rather of the precise contrary. Thousands of human beings go out of the world without ever apprehending that lines are composed of the addition or the fluxion of points. An hypothesis therefore, that is in direct opposition to so many apparent facts, must have a very uncommon portion of evidence to sustain it, if indeed it can be sustained at all.'
The true answer to this objection seems to be the following. The mind can apprehend only a single idea at once, but that idea needs not be in every sense of the word a simple idea. The mind can apprehend two or more objects at a single effort, but it cannot apprehend them as two. There seems no sufficient {327} reason to deny that all those objects which are painted at once upon the retina of the eye, produce a joint and simultaneous impression upon the mind. But they are not immediately conceived by the mind as many, but as one; so soon as the idea suggests itself that they are made up of parts, these parts cannot be considered by us otherwise than successively. The resolution of objects into their simple elements, is an operation of science and improvement; but it is altogether foreign to our first and original conceptions. In all cases the operation is rather analytical than synthetical, rather that of resolution than composition. We do not begin with the successive perception of elementary parts till we have obtained an idea of a whole; but, beginning with a whole, are capable of reducing it into its elements.
The second difficulty is of a much subtler nature. It consists in the seeming 'impossibility of performing any mental operation, such as comparison for example, which has relation to two or more ideas, if we have not both ideas before us at once, if one of them be completely vanished and gone, before the other begins to exist.' The cause of this difficulty seems to lie in the mistake of supposing that there is a real interval between the two ideas. It will perhaps be found upon an accurate examination, that, though we cannot have two ideas at once, yet it is not just to say, that the first has perished before the second begins to exist. The instant that connects them, is of no real magnitude, {328} and produces no real division. The mind is always full. It is this instant therefore that is the true point of comparison.
It may be objected, 'that this cannot be a just representation, since comparison is rather a matter of retrospect deciding between two ideas that have been completely apprehended, than a perception which occurs in the middle, before the second has been yet observed.' To this objection experience will perhaps be found to furnish the true answer. We find in fact that we cannot compare too objects till we have passed and repassed them in the mind.
'Supposing this account of the operation of the mind in comparison to be admitted, yet what shall we say to a complex sentence containing twenty ideas the sense of which I fully apprehend at a single hearing, nay, even in some cases by that time one half of it has been uttered?'
The mere task of understanding what is affirmed to us is of a very different nature from that of comparison, or any other species of judgment that is to be formed concerning this affirmation. When a number of ideas are presented in a train, though in one sense there be variety, yet in another there is a unite First, there is the unity of uninterrupted succession, the perennial flow as of a stream, where the drop indeed that succeeds is numerically distinct from that which went before, but there is no {329} cessation. Secondly, there is the unity of method. The mind apprehends, as the discourse proceeds, a strict association, from similarity or some other source, between each idea as it follows in the process, and that which went before it.
The faculty of understanding the different parts of a discourse in their connexion with each other, simple as it appears, is in reality of gradual and slow acquisition. We are by various causes excluded from a minute observation of the progress of the infant mind, and therefore do not readily conceive by how imperceptible advances it arrives at a quickness of apprehension relative to simple sentences. But we more easily remark its subsequent improvement, and perceive how long it is before it can apprehend a discourse of any length or a sentence of any abstraction.
Nothing is more certain than the possibility of my perceiving the sort of relation that exists between the different parts of a methodical discourse, for example, Mr. Burke's Speech upon Oeconomical Reform, though it be impossible for me after the severest attention to consider the several parts otherwise than successively. I have a latent feeling of this relation as the discourse proceeds, but I cannot give a firm judgment respecting it otherwise than by retrospect. It may however be suspected that, even in the case of simple apprehension, an accurate attention to the operations of mind would show that we scarcely {330} in any instance hear a single sentence, without returning again and again upon the steps of the speaker, and drawing more closely in our minds the preceding members of his period, before he arrives at his conclusion; though even this exertion of mind, subtle as it is, be not of itself thought sufficient to authorise us to give a judgment upon the whole. There may perhaps be cases where the apprehension is more instantaneous. A similar exception appears to take place even in some cases of judgment or comparison. A new association, or a connecting of two ideas by means of a middle term, which were never brought into this relation before, is a task of such a nature, that the strongest mind feels some sense of effort in the operation. But, where the judgment accurately speaking is already made, the operation is in a manner instantaneous. If you say, that a melon is a larger fruit than a cherry, I immediately assent. The judgment, though perhaps never applied to this individual subject, may be said to have been made by me long before. If again you tell me that Caesar was a worse man than Alexander, I instantly apprehend your meaning; but, unless I have upon some former occasion considered, I can neither assent nor dissent till after some reflection.
But, if the principle here stated be true, how infinitely rapid must be the succession of ideas? While I am speaking no two ideas are in my mind at the same time, and yet with what facility do I pass from one to another? If my discourse be argumentative, {331} how often do I pass the topics of which it consists in review before I utter them, and even while I am speaking continue the review at intervals without producing any pause in my discourse? How many other sensations are perceived by me during this period, without so much as interrupting, that is, without materially diverting the train of my ideas? My eye successively remarks a thousand objects that present themselves. My mind wanders to the different parts of my body, and receives a sensation from the chair upon which I sit, from the table upon which I lean; from the pinching of a shoe, from a singing in my ear, a pain in my head, or an irritation of the breast. When these most perceptibly occur, my mind passes from one to another, without feeling the minutest obstacle, or being in any degree distracted by their multiplicity. From this cursory view of the subject it appears that we have a multitude of different successive perceptions in every moment of our existence2.
Consciousness, as it has been above defined, appears to be one of the departments of memory. Now the nature of memory, so far as it relates to the subject of which we are treating, is exceedingly obvious. An infinite number of thoughts passed {332} through my mind in the last five minutes of my existence. How many of them am I now able to recollect? How many shall I recollect tomorrow? One impression after another is perpetually effacing from this intellectual register. Some of them may with great attention and effort be revived; others obtrude themselves uncalled for; and a third sort are perhaps out of the reach of any power of thought to reproduce, as having never led their traces behind them for a moment. If the memory be so capable of so many variations and degrees of intensity, may there not be some cases with which it never connects itself? If the succession of thoughts be so inexpressibly rapid, may they not pass over some topics with so delicate a touch, as to elude the supplement of consciousness?
It seems to be consciousness, rather than the succession of ideas, that measures time to the mind. The succession of ideas is in all cases exceedingly rapid, and it is by no means clear that it can be accelerated. We find it impracticable in the experiment to retain any idea in our minds unvaried for any perceptible duration. Continual flux appears to take place in every part of the universe. It is perhaps a law of our nature, that thoughts shall at all times succeed to each other with equal rapidity. Yet time seems to our apprehension to flow now with a precipitated and now with a tardy course. The indolent man reclines for hours in the shade; and, though his mind be perpetually at work, the silent lapse of duration is unobserved. {333} But, when acute pain or uneasy expectation obliges consciousness to recur with unusual force, the time then appears insupportably long. Indeed it is a contradiction in terms to suppose that the succession of thoughts, where there is nothing that perceptibly links them together, where they totally elude or instantly vanish from the memory, can be a measure of time to the mind. That there is such a state of mind in some cases assuming a permanent form, has been so much the general opinion of mankind, that it has obtained a name, and is called reverie. It is probable from what has been said that thoughts of reverie, understanding by that appellation thoughts untransmitted to the memory, perpetually take their turn with our more express and digested thoughts, even in the most active scenes of our life.
Lastly, thought may be the source of animal motion, and yet there may be no need of a distinct thought producing each individual motion. This is a very important point in the subject before us. In uttering a cry for example, the number of muscles and articulations of the body concerned in this operation is very great; shall we say the infant has a distinct thought for each motion of these articulations?
The answer to this question will be considerably facilitated, if we recollect the manner in which the impressions are blended, which we receive from external objects. The sense of feeling is diffused over every part of my body, I feel the different substances {334} that support me, the pen I guide, various affections and petty irregularities in different parts of my frame, nay, the very air that environs me. But all these impressions are absolutely simultaneous, and I can have only one perception at once. Out of these various impressions, the most powerful, or that which has the greatest advantage to solicit my attention, overcomes and drives out the rest; or, which not less frequently happens, some idea of association suggested by the last preceding idea wholly withdraws my attention from every external object. It is probable however that this perception is imperceptibly modified by the miniature impressions that accompany it, just as we actually find that the very same ideas presented to a sick man, take a peculiar tinge, that renders them exceedingly different from what they are in the mind of a man in health. It has been already shown, that, though there is nothing less frequent than the apprehending of a simple idea, yet every idea, however complex, offers itself to the mind under the conception of unity. The blending of numerous impressions into one perception is a law of our nature, and the customary train of our perceptions is entirely of this denomination. Mean while it deserves to be remarked by the way, that, at the very time that the most methodical series of perceptions is going on in the mind, there is another set of perceptions, or rather many sets playing an under or intermediate part; and, though these perpetually modify each other, yet the manner in which it is done is in an eminent degree minute and unobserved.
{335} These remarks furnish us with an answer to the long disputed question, whether the mind always thinks? It appears that innumerable impressions are perpetually made upon our body, and the only way, in which the slightest of these is prevented from conveying a distinct report to the mind, is in consequence of its being overpowered by some more considerable impression. It cannot therefore be alledged, 'that, as one impression is found to be overpowered by another while we wake, the strongest only of the simultaneous impressions furnishing an idea to the mind; so the whole set of simultaneous impressions during sleep may be overpowered by some disposition of the sensorium, and entirely fail of its effect.' For, first, the cases are altogether different. From the explication above given it appeared, that not one of the impressions was really lost, but tended, though in a very limited degree, to modify the predominant impression. Secondly, nothing can be more unintelligible than this indisposition. Were it of the nature which the objection requires, sleep ought to cease of its own accord after the expiration of a certain term, but to be incapable of interruption from any experiment I might make upon the sleeper. To what purpose call or shake him? Shall we say, that it requires an impression of a certain magnitude to excite the sensorium? But a clock shall strike in the room and not wake him, when a voice of much lower key produces that effect. What is the precise degree of magnitude necessary? We actually find the ineffectual calls that are addressed to us, as well as various other sounds, occasionally {336} mixing with our dreams, without our being aware from whence this new perception arose.
To apply these observations. If a number of impressions come blended to the mind, so as to make up one thought or perception, why may not one thought, in cases where the mind acts as a cause, produce a variety of motions? It has already been shown that there is no essential difference between the two cases. The mind is completely passive in both. Is there any sufficient reason to show, that, though it be possible for one substance considered as the recipient of effects to be the subject of a variety of simultaneous impressions, yet it is impossible for one substance considered as a cause to produce a variety of simultaneous motions? If it be granted that there is not, if the mere modification of a thought designing a motion in chief, may produce a secondary motion, then it must perhaps farther be confessed possible for that modification which my first thought produced in my second, to carry on the motion, even though the second thought be upon a subject altogether different.
The consequences, which seem deducible from this theory of mind, are sufficiently memorable. By showing the extreme subtlety and simplicity of thought, it removes many of the difficulties that might otherwise rest upon its finer and more evanescent operation. If thought, in order to be the cause of animal motion, need not have either the nature of volition, or the {337} concomitant of consciousness, and if a single thought may become a complex cause and produce a variety of motions, it will then become exceedingly difficult to trace its operations, or to discover any circumstances in a particular instance of animal motion, which can sufficiently indicate that thought was not the principle of its production, and by that means supersede the force of the general arguments adduced at the beginning of this chapter. Hence therefore it appears that all those motions which are observed to exist in substances having perception, and which are not to be discovered in substances of any other species, may reasonably be suspected to have thought, the distinguishing peculiarity of such substances, for their cause.
There are various classes of motion which will fall under this definition, beside those already enumerated. An example of one of those classes suggests itself in the phenomenon of walking. An attentive observer will perceive various symptoms calculated to persuade him, that every step he takes during the longest journey is the production of thought. Walking is in all cases originally a voluntary motion. In a child when he learns to walk, in a rope dancer when he begins to practise that particular exercise, the distinct determination of mind preceding every step is sufficiently perceptible. It may be absurd to say, that a long series of motion can be the result of so many express volitions, when these supposed volitions leave no trace in the memory. But it is not unreasonable to believe, that a {338} species of motion which began in express design, may, though it ceases to be the subject of conscious attention, owe its continuance to a continued series of thoughts flowing in that direction, and that, if life were taken away, material impulse would not carry on the exercise for a moment. We actually find, that, when our thoughts in a train are more than commonly earnest, our pace slackens, and sometimes our going forward is wholly suspended, particularly in any less common species of walking, such as that of descending a flight of stairs. In ascending the case is still more difficult, and accordingly we are accustomed to suspend the regular process of reflection during that operation.
Another class of motions of a still subtler nature, are the regular motions of the animal economy, such as the circulation of the blood, and the pulsation of the heart. Are thought and perception the medium of these motions? We have the same argument here as in the former instances, conjunction of event. When thought begins, these motions also begin; and, when it ceases, they are at an end. They are therefore either the cause or effect of percipiency, or mind; but me shall be inclined to embrace the latter side of this dilemma, when we recollect that we are probably acquainted with many instances in which thought is the immediate cause of motions, which scarcely yield in subtlety to these; but that, as to the origin of thought, we are wholly uninformed. Add to this, that there are probably {339} no motions of the animal economy, which we do not find it in the power of volition, and still more of involuntary sensations, to hasten or retard.
It is far from certain that the phenomenon of motion can any where exist where there is not thought. Motion may be distributed into four classes; the simpler motions which result from what are called the essential properties of matter and the laws of impulse; the more complex ones which cannot be accounted for by the assumption of these laws, such as gravitation, elasticity, electricity and magnetism; and the motions of the vegetable and animal systems. Each of these seems farther than that which preceded it from being able to be accounted for by any thing we understand of the nature of matter.
Some light may be derived from what has been here advanced upon the phenomenon of dreams. 'In sleep we sometimes imagine' for example 'that we read long passages from books, or hear a long oration from a speaker. In all cases scenes and incidents pass before us that in various ways excite our passions and interest our feelings. Is it possible that these should be the unconscious production of our own minds?'
It has already appeared, that volition is the accidental, and by no means the necessary concomitant, even of those thoughts which are most active and efficient in the producing of motion. {340} It is therefore no more to be wondered at that the mind should be busied in the composition of books which it appears to read, than that a train of thoughts of any other kind should pass through it without a consciousness of its being the author. In fact we perpetually annex wrong and erroneous ideas to this phrase, that we are the authors. Though mind be a real and efficient cause, it is in no case a first cause. It is the medium through which operations are produced. Ideas succeed each other in our sensorium according to certain necessary laws. The most powerful impression, either from without or from within, constantly gets the better of all its competitors, and forcibly drives out the preceding thought, till it is in the same irresistible manner driven out by its successor.
2. An attempt has been made to calculate these, but there is no reason to believe that the calculation deserves to be considered as a standard of truth. Sensations leave their images behind them, some for a longer and some for a shorter time; so that, in two different instances, the calculation is in one case eight, and in another three hundred and twenty to a second.