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ESSAYS ON THE INTELLECTUAL POWERS OF MAN *-*
by
Thomas Reid
(1785)

CHAPTER 14: REFLECTIONS ON THE COMMON THEORY OF IDEAS

After so long a detail of the sentiments of philosophers, ancient and modern, concerning ideas, it may seem presumptuous to call in question their existence. But no philosophical opinion, however ancient, however generally received, ought to rest upon authority. There is no presumption in requiring evidence for it, or in regulating our belief by the evidence we can find.

To prevent mistakes, the reader must again be reminded that if by ideas are meant only the acts or operations of our minds in perceiving, remembering, or imagining objects, I am far from calling in question the existence of those acts; we are conscious of them every day and every hour of life; and I believe no man of a sound mind ever doubted of the real existence of the operations of mind, of which he is conscious. Nor is it to be doubted that, by the faculties which God has given us, we can conceive things that are absent as well as perceive those that are within the reach of our senses; and that such conceptions may be more or less distinct, and more or less lively and strong. We have reason to ascribe to the all-knowing and all-perfect Being distinct conceptions of all things existent and possible, and of all their relations; and if these conceptions are called his eternal ideas, there ought to be no dispute among philosophers about a word. The ideas, of whose existence I require the proof, are not the operations of any mind, but supposed objects of those operations. They are not perception, remembrance, or conception, but things that are said to be perceived, or remembered, or imagined.

Nor do I dispute the existence of what the vulgar call the objects of perception. These, by all who acknowledge their existence, are called real things, not ideas. But philosophers maintain that, besides these, there are immediate objects of perception in the mind itself: that, for instance, we do not see the sun immediately, but an idea; or, as Mr. Hume calls it, an impression in our own minds. This idea is said to be the image, the resemblance, the representative of the sun, if there be a sun. It is from the existence of the idea that we must infer the existence of the sun. But the idea, being immediately perceived, there can be no doubt, as philosophers think, of its existence.

In like manner, when I remember, or when I imagine anything, all men acknowledge that there must be something that is remembered or that is imagined; that is, some object of those operations. The object remembered must be something that did exist in time past: the object imagined may be something that never existed. But, say the philosophers, besides these objects which all men acknowledge, there is a more immediate object which really exists in the mind at the same time we remember or imagine. This object is an idea or image of the thing remembered or imagined.

The first reflection I would make on this philosophical opinion is, that it is directly contrary to the universal sense of men who have not been instructed in philosophy. When we see the sun or moon, we have no doubt that the very objects which we immediately see are very far distant from us, and from one another. We have not the least doubt that this is the sun and moon which God created some thousands of years ago, and which have continued to perform their revolutions in the heavens ever since. But how are we astonished when the philosopher informs us that we are mistaken in all this; that the sun and moon which we see are not, as we imagine, many miles distant from us, and from each other, but they are in our own mind; that they had no existence before we saw them, and will have none when we cease to perceive and to think of them; because the objects we perceive are only ideas in our own mind, which can have no existence a moment longer than we think of them!

If a plain man, uninstructed in philosophy, has faith to receive these mysteries, how great must be his astonishment! He is brought into a new world where everything he sees, tastes, or touches, is an idea - a fleeting kind of being which he can conjure into existence, or can annihilate in the twinkling of an eye.

After his mind is somewhat composed, it will be natural for him to ask his philosophical instructor, Pray, sir, are there then no substantial and permanent beings called the sun and moon, which continue to exist whether we think of them or not?

Here the philosophers differ. Mr. Locke, and those that were before him, will answer to this question that it is very true there are substantial and permanent beings called the sun and moon; but they never appear to us in their own person, but by their representatives, the ideas in our own minds, and we know nothing of them but what we can gather from those ideas.

Bishop Berkeley and Mr. Hume would give a different answer to the question proposed. They would assure the querist that it is a vulgar error, a mere prejudice of the ignorant and unlearned, to think that there are any permanent and substantial beings called the sun and moon; that the heavenly bodies, our own bodies, and all bodies whatsoever, are nothing but ideas in our minds; and that there can be nothing like the ideas of one mind, but the ideas of another mind. There is nothing in nature but minds and ideas, says the Bishop; - nay, says Mr. Hume, there is nothing in nature but ideas only; for what we call a mind is nothing but a train of ideas connected by certain relations between themselves.

In this representation of the theory of ideas there is nothing exaggerated or misrepresented, as far as I am able to judge; and surely nothing further is necessary to show that, to the uninstructed in philosophy, it must appear extravagant and visionary, and most contrary to the dictates of common understanding.

There is the less need of any further proof of this, that it is very amply acknowledged by Mr. Hume in his Essay on the Academical or Sceptical Philosophy. ⁽¹⁾

It is therefore acknowledged by this philosopher to be a natural instinct or prepossession, a universal and primary opinion of all men, a primary instinct of nature, that the objects which we immediately perceive by our senses are not images in our minds, but external objects, and that their existence is independent of us and our perception.

In this acknowledgment Mr. Hume indeed seems to me more generous, and even more ingenuous, than Bishop Berkeley, who would persuade us that his opinion does not oppose the vulgar opinion, but only that of the philosophers; and that the external existence of a material world is a philosophical hypothesis, and not the natural dictate of our perceptive powers.

A second reflection upon this subject is - that the authors who have treated of ideas have generally taken their existence for granted, as a thing that could not be called in question; and such arguments as they have mentioned incidentally, in order to prove it, seem too weak to support the conclusion.

Mr. Locke, in the Introduction to his Essay, ⁽²⁾ tells us that he uses the word idea to signify whatever is the immediate object of thought; and then adds, "I presume it will be easily granted me that there are such ideas in men's minds; everyone is conscious of them in himself; and men's words and actions will satisfy him that they are in others." I am indeed conscious of perceiving, remembering, imagining; but that the objects of these operations are images in my mind, I am not conscious. I am satisfied, by men's words and actions, that they often perceive the same objects which I perceive, which could not be if those objects were ideas in their own minds.

Mr. Norris ⁽³⁾ is the only author I have met with who professedly puts the question whether material things can be perceived by us immediately. He has offered four arguments to show that they cannot. First, "Material objects are without the mind, and therefore there can be no union between the object and the percipient." Answer, This argument is lame, until it is shown to be necessary that in perception there should be a union between the object and the percipient. Second, "Material objects are disproportioned to the mind, and removed from it by the whole diameter of Being." This argument I cannot answer, because I do not understand it. Third, "Because, if material objects were immediate objects of perception, there could be no physical science - things necessary and immutable being the only object of science." Answer, Although things necessary and immutable be not the immediate objects of perception, they may be immediate objects of other powers of the mind. Fourth, "If material things were perceived by themselves, they would be a true light to our minds, as being the intelligible form of our understandings, and consequently perfective of them, and indeed superior to them." If I comprehend anything of this mysterious argument, it follows from it that the Deity perceives nothing at all, because nothing can be superior to his understanding or perfective of it.

There is an argument which is hinted at by Malebranche, and by several other authors, which deserves to be more seriously considered. As I find it most clearly expressed and most fully urged by Dr. Samuel Clarke, ⁽⁴⁾ I shall give it in his words, in his second reply to Leibniz, § 4: "The soul, without being present to the images of the things perceived, could not possibly perceive them. A living substance can only there perceive, where it is present, either to the things themselves (as the omnipresent God is to the whole universe) or to the images of things, as the soul is in its proper sensorium."

Sir Isaac Newton expresses the same sentiment, but with his usual reserve, in a query only.

The ingenious Dr. Porterfield, in his Essay concerning the Motions of our Eyes, adopts this opinion with more confidence. His words are: "How body acts upon mind, or mind upon body, I know not; but this I am very certain of, that nothing can act, or be acted upon, where it is not; and therefore our mind can never perceive anything but its own proper modifications, and the various states of the sensorium, to which it is present: so that it is not the external sun and moon which are in the heavens, which our mind perceives, but only their image or representation impressed upon the sensorium. How the soul of a seeing man sees these images, or how it receives those ideas, from such agitations in the sensorium, I know not; but I am sure it can never perceive the external bodies themselves, to which it is not present."

These, indeed, are great authorities: but in matters of philosophy we must not be guided by authority, but by reason. Dr. Clarke, in the place cited, mentions slightly, as the reason of his opinion, that "nothing can any more act, or be acted upon when it is not present, that it can be where it is not." And again, in his third reply to Leibniz, § 11: "We are sure the soul cannot perceive what it is not present to, because nothing can act, or be acted upon, where it is not." The same reason we see is urged by Dr. Porterfield.

That nothing can act immediately where it is not, I think must be admitted: for I agree with Sir Isaac Newton, that power without substance is inconceivable. It is a consequence of this, that nothing can be acted upon immediately where the agent is not present: let this, therefore, be granted. To make the reasoning conclusive, it is further necessary that, when we perceive objects, either they act upon us or we act upon them. This does not appear self-evident, nor have I ever met with any proof of it. I shall briefly offer the reasons why I think it ought not to be admitted.

When we say that one being acts upon another, we mean that some power or force is exerted by the agent which produces, or has a tendency to produce, a change in the thing acted upon. If this be the meaning of the phrase, as I conceive it is, there appears no reason for asserting that, in perception, either the object acts upon the mind or the mind upon the object.

An object, in being perceived, does not act at all. I perceive the walls of the room where I sit; but they are perfectly inactive, and therefore act not upon the mind. To be perceived is what logicians call an external denomination which implies neither action nor quality in the object perceived. Nor could men ever have gone into this notion that perception is owing to some action of the object upon the mind, were it not that we are so prone to form our notions of the mind from some similitude we conceive between it and body. Thought in the mind is conceived to have some analogy to motion in a body: and as a body is put in motion by being acted upon by some other body, so we are apt to think the mind is made to perceive by some impulse it receives from the object. But reasonings drawn from such analogies ought never to be trusted. They are, indeed, the cause of most of our errors with regard to the mind. And we might as well conclude that minds may be measured by feet and inches, or weighed by ounces and drams; because bodies have those properties.

I see as little reason, in the second place, to believe that in perception the mind acts upon the object. To perceive an object is one thing, to act upon it is another; nor is the last at all included in the first. To say that I act upon the wall by looking at it is an abuse of language, and has no meaning. Logicians distinguish two kinds of operations of mind: the first kind produces no effect without the mind; the last does. The first they call immanent acts, the second transitive. All intellectual operations belong to the first class; they produce no effect upon any external object. But, without having recourse to logical distinctions, every man of common sense knows that to think of an object, and to act upon it, are very different things.

As we have, therefore, no evidence that in perception the mind acts upon the object, or the object upon the mind, but strong reasons to the contrary, Dr. Clarke's argument against our perceiving external objects immediately falls to the ground.

This notion that, in perception, the object must be contiguous to the percipient seems, with many other prejudices, to be borrowed from analogy. In all the external senses there must, as has been before observed, be some impression made upon the organ of sense by the object, or by something coming from the object. An impression supposes contiguity. Hence we are led by analogy to conceive something similar in the operations of the mind.

When we lay aside those analogies and reflect attentively upon our perception of the object of sense, we must acknowledge that, though we are conscious of perceiving objects, we are altogether ignorant how it is brought about, and know as little how we perceive objects as how we were made. And, if we should admit an image in the mind, or contiguous to it, we know as little how perception may be produced by this image as by the most distant object. Why, therefore, should we be led, by a theory which is neither grounded on evidence nor, if admitted, can explain any one phenomenon of perception, to reject the natural and immediate dictates of those perceptive powers to which, in the conduct of life, we find a necessity of yielding implicit submission?

There remains only one other argument that I have been able to find urged against our perceiving external objects immediately. It is proposed by Mr. Hume, who, in the essay already quoted, after acknowledging that it is a universal and primary opinion of all men that we perceive external objects immediately, subjoins what follows:

But this universal and primary opinion of all men is soon destroyed by the slightest philosophy, which teaches us that nothing can ever be present to the mind but an image or perception; and that the senses are only the inlets through which these images are received, without being ever able to produce any immediate intercourse between the mind and the object. The table, which we see, seems to diminish as we remove further from it: but the real table, which exists independent of us, suffers no alteration. It was, therefore, nothing but its image which was present to the mind. These are the obvious dictates of reason; and no man who reflects ever doubted that the existences which we consider, when we say this house and that tree, are nothing but perceptions in the mind, and fleeting copies and representations of other existences, which remain uniform and independent. So far, then, we are necessitated, by reasoning, to depart from the primary instincts of nature, and to embrace a new system with regard to the evidence of our senses.

We have here a remarkable conflict between two contradictory opinions, wherein all mankind are engaged. On the one side stand all the vulgar, who are unpractised in philosophical researches, and guided by the uncorrupted primary instincts of nature. On the other side stand all the philosophers, ancient and modern; every man, without exception, who reflects. In this division, to my great humiliation, I find myself classed with the vulgar.

The passage now quoted is all I have found in Mr. Hume's writings upon this point: and, indeed, there is more reasoning in it than I have found in any other author. I shall, therefore, examine it minutely.

First, He tells us that "this universal and primary opinion of all men is soon destroyed by the slightest philosophy, which teaches us that nothing can ever be present to the mind but an image or perception."

The phrase of being present to the mind has some obscurity, but I conceive he means being an immediate object of thought; an immediate object, for instance, of perception, of memory, or of imagination. If this be the meaning (and it is the only pertinent one I can think of), there is no more in this passage but an assertion of the proposition to be proved, and an assertion that philosophy teaches it. If this be so, I beg leave to dissent from philosophy till she gives me reason for what she teaches. For, though common sense and my external senses demand my assent to their dictates upon their own authority, yet philosophy is not entitled to this privilege. But, that I may not dissent from so grave a personage without giving a reason, I give this as the reason of my dissent: I see the sun when he shines; I remember the battle of Culloden; and neither of these objects is an image or perception.

He tells us, in the next place, "That the senses are only the inlets, through which these images are received."

I know that Aristotle and the schoolmen taught that images or species flow from objects, and are let in by the senses, and strike upon the mind; but this has been so effectually refuted by Descartes, by Malebranche, and many others, that nobody now pretends to defend it. Reasonable men consider it as one of the most unintelligible and unmeaning parts of the ancient system. To what cause is it owing that modern philosophers are so prone to fall back into this hypothesis, as if they really believed it? For of this proneness I could give many instances besides this of Mr. Hume; and I take the cause to be that images in the mind, and images let in by the senses, are so nearly allied, and so strictly connected, that they must stand or fall together. The old system consistently maintained both: but the new system has rejected the doctrine of images let in by the senses, holding, nevertheless, that there are images in the mind; and, having made this unnatural divorce of two doctrines which ought not to be put asunder, that which they have retained often leads them back involuntarily to that which they have rejected.

Mr. Hume surely did not seriously believe that an image of sound is let in by the ear, an image of smell by the nose, an image of hardness and softness, of solidity and resistance, by the touch. For besides the absurdity of the thing, which has often been shown, Mr. Hume and all modern philosophers maintain that the images which are the immediate objects of perception have no existence when they are not perceived; whereas if they were let in by the senses, they must be, before they are perceived, and have a separate existence.

He tells us, further, that philosophy teaches that the senses are unable to produce any immediate intercourse between the mind and the object. Here I still require the reasons that philosophy gives for this; for, to my apprehension, I immediately perceive external objects, and this I conceive is the immediate intercourse here meant.

Hitherto I see nothing that can be called an argument. Perhaps it was intended only for illustration. The argument, the only argument, follows:

The table which we see, seems to diminish as we remove farther from it; but the real table, which exists independent of us, suffers no alteration. It was, therefore, nothing but its image which was presented to the mind. These are the obvious dictates of reason.

Let us suppose, for a moment, that it is the real table we see: Must not this real table seem to diminish as we remove farther from it? It is demonstrable that it must. How then can this apparent diminution be an argument that it is not the real table? When that which must happen to the real table, as we remove farther from it, does actually happen to the table we see, it is absurd to conclude from this, that it is not the real table we see. It is evident, therefore, that this ingenious author has imposed upon himself by confounding real magnitude with apparent magnitude, and that his argument is a mere sophism.

I observed that Mr. Hume's argument not only has no strength to support his conclusion, but that it leads to the contrary conclusion - to wit, that it is the real table we see; for this plain reason, that the table we see has precisely that apparent magnitude which it is demonstrable the real table must have when placed at that distance.

This argument is made much stronger by considering that the real table may be placed successively at a thousand different distances, and, in every distance, in a thousand different positions; and it can be determined demonstratively, by the rules of geometry and perspective, what must be its apparent magnitude and apparent figure in each of those distances and positions. Let the table be placed successively in as many of those different distances and different positions as you will, or in them all; open your eyes and you shall see a table precisely of that apparent magnitude, and that apparent figure, which the real table must have in that distance and in that position. Is not this a strong argument that it is the real table you see?

In a word, the appearance of a visible object is infinitely diversified according to its distance and position. The visible appearances are innumerable when we confine ourselves to one object, and they are multiplied according to the variety of objects. Those appearances have been matter of speculation to ingenious men at least since the time of Euclid. They have accounted for all this variety, on the supposition that the objects we see are external and not in the mind itself. The rules they have demonstrated about the various projections of the sphere, about the appearances of the planets in their progressions, stations, and retrogradations, and all the rules of perspective, are built on the supposition that the objects of sight are external. They can each of them be tried in thousands of instances. In many arts and professions innumerable trials are daily made; nor were they ever found to fail in a single instance. Shall we say that a false supposition, invented by the rude vulgar, has been so lucky in solving an infinite number of phenomena of nature? This, surely, would be a greater prodigy than philosophy ever exhibited: add to this, that, upon the contrary hypothesis - to wit, that the objects of sight are internal - no account can be given of any one of those appearances, nor any physical cause assigned why a visible object should, in any one case, have one apparent figure and magnitude rather than another. Thus, I have considered every argument I have found advanced to prove the existence of ideas, or images of external things, in the mind; and, if no better arguments can be found, I cannot help thinking that the whole history of philosophy has never furnished an instance of an opinion so unanimously entertained by philosophers upon so slight grounds.

A third reflection I would make upon this subject is, that philosophers, notwithstanding their unanimity as to the existence of ideas, hardly agree in any one thing else concerning them. If ideas be not a mere fiction, they must be, of all objects of human knowledge, the things we have best access to know, and to be acquainted with; yet there is nothing about which men differ so much. Some have held them to be self-existent, others to be in the Divine mind, others in our own minds, and others in the brain or sensorium. I considered the hypothesis of images in the brain, in the fourth chapter of this essay. As to images in the mind, if anything more is meant by the image of an object in the mind than the thought of that object, I know not what it means. The distinct conception of an object may, in a metaphorical or analogical sense, be called an image of it in the mind. But this image is only the conception of the object, and not the object conceived. It is an act of the mind, and not the object of that act.

Some philosophers will have our ideas, or a part of them, to be innate; others will have them all to be adventitious: some derive them from the senses alone; others from sensation and reflection: some think they are fabricated by the mind itself; others that they are produced by external objects; others that they are the immediate operation of the Deity; others say that impressions are the causes of ideas, and that the causes of impressions are unknown: some think that we have ideas only of material objects, but none of minds, of their operations, or of the relations of things; others will have the immediate object of every thought to be an idea: some think we have abstract ideas, and that by this chiefly we are distinguished from the brutes; others maintain an abstract idea to be an absurdity, and that there can be no such thing: with some they are the immediate objects of thought, with others the only objects.

A fourth reflection is, that ideas do not make any of the operations of the mind to be better understood, although it was probably with that view that they have been first invented, and afterwards so generally received. We are at a loss to know how we perceive distant objects; how we remember things past; how we imagine things that have no existence. Ideas in the mind seem to account for all these operations: they are all by the means of ideas reduced to one operation - to a kind of feeling, or immediate perception of things present and in contact with the percipient; and feeling is an operation so familiar that we think it needs no explication, but may serve to explain other operations.

But this feeling, or immediate perception, is as difficult to be comprehended as the things which we pretend to explain by it. Two things may be in contact without any feeling or perception; there must therefore be in the percipient a power to feel or to perceive. How this power is produced, and how it operates, is quite beyond the reach of our knowledge. As little can we know whether this power must be limited to things present, and in contact with us. Nor can any man pretend to prove that the Being who gave us the power to perceive things present may not give us the power to perceive things that are distant, to remember things past, and to conceive things that never existed.

Some philosophers have endeavoured to make all our senses to be only different modifications of touch; a theory which serves only to confound things that are different, and to perplex and darken things that are clear. The theory of ideas resembles this, by reducing all the operations of the human understanding to the perception of ideas in our own minds. This power of perceiving ideas is as inexplicable as any of the powers explained by it; and the contiguity of the object contributes nothing at all to make it better understood; because there appears no connection between contiguity and perception, but what is grounded on prejudices drawn from some imagined similitude between mind and body, and from the supposition that, in perception, the object acts upon the mind, or the mind upon the object. We have seen how this theory has led philosophers to confound those operations of mind which experience teaches an men to be different, and teaches them to distinguish in common language; and that it has led them to invent a language inconsistent with the principles upon which all language is grounded.

1. An Enquiry Concerning Human Understanding, Section XII (1748).

2. An Essay Concerning Human Understanding (1690).

3. John Norris (1657-1711), an English disciple of Nicolas Malebranche (1638-1715) associated with the Cambridge Platonists. Essay towards the Theory of the Ideal and the Sensible World (Vol. I, 1701; Vol. II, 1704).

4. (1675-1729). The correspondences with Leibniz consisted of five letters by Leibniz and five replies by Clarke during the period 1715-16. These were published by Clarke in 1717 following the death of Leibniz (1716).

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