Book 4, Chapter 09 : Of the Mechanism of the Human Mind
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Book 4, Chapter 09
Nature of Mechanism. - Its classes, material and intellectual. - Material system, or of vibra- tions. - 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 pro- duce animal motion may be - I. involuntary - 2. unattended witk 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 oper- ations - as comparison - apprehension. - Rapidity of the succession of ideas. - Appli- cation. - 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. - OS dreams.
THE doctrine of necessity being admitted, it follows that the theory of the human mind is properly, like the theory of every other series of events with which we are acquainted, a system of mechanism; understanding by mechanism nothing more than a regular succession of phenomena, without any uncertainty of event, so that every consequent requires a specific antecedent, and could be no otherwise in any respect than as the antecedent 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, the other which has for its medium thought. Which of these is to be regarded as 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. 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 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 certain convulsive and spasmodic affections appear 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 pressed in a certain manner, utters a groan, without anything 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 traces happen to approach or run into each other; and we have then a complete scheme of a certain sort, of 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, in the author of the universe for example, to introduce a thinking substance, or a power of perception, as a spectator of the process. But this percipient power is altogether neutral, having apparently no concern, either as a medium or otherwise, in the events to be produced.1
The second system, which represents thought as the medium of operation, is not less a system of mechanism according to the doctrine of necessity, 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 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 shown to be the only ground we have, in any imaginable subject, for proceeding from antecedent to consequent, and expecting, when we see one given event, that another event of a given sort will succeed it.2 We cannot therefore reject the principle which supposes thought to be a real medium in the mechanism of man, but upon grounds that would vitiate our reasonings in every topic of human inquiry.
It may be objected 'that, though this regularity of event is the only rational principle of inference, yet thought may be found not to possess the character of a medium, motion being in all instances the antecedent, and thought never anything more than a consequent'. But this is contrary to everything we know of the system of the universe, in which each event appears to be alternately both the one and the other, nothing terminating in itself, but everything 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 promotion in the animal system'; since it has just appeared that this ignorance is by no means peculiar to the subject before us. We are universally unable to perceive a foundation of necessary connection.3
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 cartied 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.4 Such, for example, are the cries of an infant, when it is first impressed with the sensation of pain. 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 these motions have sensation or thought for their constant concomitant; and therefore all the arguments which have been already alleged remain in full force, to prove that thought is the medium of their production.
Nor will this appear 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 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; and my hand is necessarily stretched out with an intention to obtain it. If a perception of preference, or desirableness, irresistibly lead to 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 no longer afford the slightest ground to expect motion in the links that were after. - It is possible that, as a numerous class of motions have their constant origin in thought, so there may be no thoughts altogether unattended with motion.
Secondly, thought may be the source of animal motion and at the same time be unattended with consciousness This is undoubtedly a distinction of considerable refine-. meet, depending upon the precise 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 of the nature of an intuitive axiom; and experience is perpetually reminding us of its truth. In comparing two objects, we frequently endeavor, as it were, to draw them together in the mind, but we seem obliged to pass successively from the one to the other.
But, though it be intuitively true that we can attend to but one thing, or, in other words, have but one thought, at one time, and though intuitive and self-evident propositions do not, properly speaking, admit of being supported by argument, yet there is a collateral consideration, something in the nature of an argument, that may be adduced in support of this proposition. It is at present generally admitted, by all accurate reasoners upon the nature of the human mind, that its whole internal history may be traced to one single principle, association. There are but two ways in which a thought can be excited in the mind, first, by external impression, secondly, by the property which one thought existing in the mind is found to have, of introducing a second thought through the means of some link of connection between them. This being premised, let us suppose a given mind to have two ideas at the same time. There can be no reason why either of these ideas should prove ungenerative, or why the two ideas they are best fitted to bring after them should not coexist as well as their predecessors. Let the same process be repeated indefinitely. We have then two trains of thinking exactly contemporary in the same mind. Very curious questions will here arise. Have they any communication? Do they flow separately, or occasionally cross and interrupt each other? Can any reason be given, why one of them should not relate to the doctrine of fluxions, and the other to the drama? in other words, why the same man should not, at the same time, be both Newton and Shakespeare? Why may not one of these coexisting trains be of a joyful and the other of a sorrowful tenor? There is no absurdity that may not be supported upon the assumption of this principle. In fact we have no other conception of fidelity, as it relates to the human mind, than that of a single idea, supersedable by external impression, or regularly leading on, by means of various connections, to an indefinite train of ideas in uninterrupted succession.
But this principle, though apparently supported both by reason and intuition, 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 it relates to visible objects. '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 or 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 that 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, to 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 fluxion of points. An hypothesis 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.'
The true answer to this objection seems to be as follows. The mind can apprehend only a single idea at once, but that idea needs not be 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 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: the recollection may occur that they are made up of parts, but 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 operations of our understanding are rather analytical than synthetical, rather those 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.
A 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 exit'. The source 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, 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 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 observed'. To this objection experience will perhaps be found to furnish the true answer. We find in fact that we cannot compare two 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 the time one half of it has been uttered?'
The mere talk of understanding what is affirmed to us is of a very different nature from that of comparison, or of 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 unity. 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 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 connection 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 the simplest sentences. But we more easily remark its subsequent improvement, and perceive how long it is, before it can apprehend a discourse of considerable length, or a sentence of great 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, even in the case of simple apprehension, that an accurate attention to the operations of the mind would show that we scarcely 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 its conclusion; though even this exertion of mind, subtle as it is, be not of itself thought sufficient to authorize us to give a judgment of the whole.
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, how often do I pass in review the topics of which it consists, 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 experienced 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, or 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 existence.5 - To return.
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 obvious. An infinite number of thoughts passed through my mind in the last five minutes of my existence. How many of them am I now able to recollect? How many of them 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 left their traces behind them for a moment. If the memory be 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 thought 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 mind unvaried for any perceptible duration. Continual flux appears to take place in every part of the universe. Of thought, may be said, in a practical sense, what has been affirmed of matter, that it is infinitely divisible. 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 progress of time is unobserved. But, when acute pain, or uneasy expectation, obliges consciousness to recur with unusual force, the time 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 the memory and instantly vanish, 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 essential 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 that the infant has a distinct thought for each 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 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 which accompany it, just as we actually find that the very same ideas presented to a sick man take a peculiar tinge which 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. After this manner, not only every perception is complicated by a variety of simultaneous impressions, but every idea that now offers itself to the mind is modified by all the ideas that ever existed in it. It is this circumstance that constitutes the insensible empire of prejudice; and causes every object which is exhibited to a number of individuals to assume as many forms in their mine as there are individuals who view it.
These remarks furnish us with an answer to the long disputed question, whether the mind always thinks? It appears that innumerable impressions are perpetual!' 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 alleged '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 indisposition 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 absurd than this supposition. Sleep ought, according to this scheme, to cease of itself 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? This act evinces my knowledge, and its success the truth of my knowledge, that he is in a state susceptible of impression. But, if susceptible of impression, then impressed, by bedclothes, etc. Shall we say, 'that it requires an impression of a certain magnitude to excite the sensorium'? But a dock shall strike in the room and not wake him, when a voice of a 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 mixing with our dreams, without our being aware from whence these new perceptions arose. Thus it appears that every, the most minute, impression that is made upon our bodies in a state of sleep or deliquium is conveyed to the mind, however faint may be its effect, or however it may be overpowered and swallowed up by other sensations or circumstances.
Let it however be observed that the question whether the mind always thinks is altogether different from the question, which has sometimes been confounded with it, whether a sleeping man always dreams. The arguments here adduced seem conclusive as to the first question, but there is some reason to believe that there have been men who never once dreamed in the whole course of their lives.
To apply these observations. If a number of impressions acting upon the mind may come to us so blended as to make up one thought or perception, why may not one thought, in cases where the mind acts as a principle, 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 (a cry, for example, or a motion of the limbs), may produce a secondary motion, then it must perhaps further 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 operations. If thought, in order to be the source of animal motion, need not have either the nature of volition, or the concomitant of consciousness, and if a single thought may become a complex source, 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 in 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 source.
There are various classes of motion which will fall under this definition, beside those already enumerated. An example of one of these 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 practice that particular exercise, the distinct determination of mind, preceding each step, is sufficiently perceptible. It may be absurd to say that a long series of motions 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 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 wholly to suspend the regular progress 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 we 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 the faculty of thought, we are wholly uninformed. Add to this that there are probably no motions of the animal economy which we do not find it in the power of volition, and still more of our involuntary sensations, to hasten or retard.
It is far from certain that the phenomenon of motion can anywhere 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, the motions of the vegetable, and of the animal systems. Each of these seems further than that which preceded it, from being accounted for by anything 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. 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 erroneous ideas to this phrase, that we are the authors. Though mind be a real and proper antecedent, it is in no case a first cause, a thing indeed of which we have in no case any experimental knowledge. Thought 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 within, constantly gets the better of its competitors, and forcibly drives out the preceding thought, till it is in the same irresistible manner driven out by its successor.
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