These two doctrines are in a sense the exact antithesis of one another. They agree together in this, that in each the explanation of error follows as a consequence of the conception of the nature of truth. The pragmatist theory implies that there is no truth in any real sense, but only more or less successful error. The idealist theory implies that there is no real error, but only a variety in the degree of truth.

Most people, however, are convinced that truth and error are not related to one another, nor to the circumstances that call forth belief or disbelief. Let us now examine a theory that recognises this. There are false judgments, and they need explanation; error has a nature of its own. If a judgment is false, it is absolutely and unalterably false; if it is true, it is unconditionally true and with no reserve. No logical process, no psychological disposition, can make what is false true. Error must lie in the nature of knowledge, and to discover that nature we must understand the theory of knowledge and determine the exact nature of the mental act in knowing. The first essential is to distinguish the kind of knowledge to which truth and error can apply. We pointed out in the second chapter that all knowledge rests ultimately on immediate experience. In immediate experience the relation between the mental act of knowing and the object that is known is so simple that any question as to truth or error in regard to it is unmeaning. To question the truth of immediate experience is to question its existence; it is to ask if it is what it is, and this is plainly unmeaning. But thinking, we said, is questioning experience in order to know its content or meaning, and in thinking, the simplicity of the relation which unites the mind to its object in immediate experience is left behind, and a logical process of very great complexity takes its place. It is in this complexity that the possibility of error lies.

Let us look at it a little more closely. Knowing is a relation which unites two things, one the mind that knows, the other the thing known. In every act of knowing, something is present to the mind; if knowing is simply awareness of this actually present something, we call it immediate experience, we are acquainted with the object. But our knowledge is not only of objects immediately present to the mind and with which we are therefore acquainted. Knowledge embraces the past and future and the distant realms of space. Indeed were knowledge only of what is actually present to the mind, it is difficult to imagine that we could, in the ordinary meaning of the word, know anything at all. I may be thinking, for example, of an absent friend; all that is present to my mind is, it may be, a memory image, a faint recall of his appearance on some one occasion, or perhaps a recollection of the tone of his voice, or it may be the black marks on white paper which I recognise as his handwriting. This image is present to my mind, but the image is not the object, my friend, about whom I think and make endless judgments, true and false. So also, if what is present to the mind is affecting me through the external senses, if it is a sense impression, it is clear that what is actually present is not the whole object of which I am aware, but only a very small part of it, or, it may be, no part of it at all, but something, a sound, or an odour, that represents it. The immediate data of consciousness are named by some philosophers sense data, by others, presentations, by others images, and there is much controversy as to their nature and existence, but with this controversy we are not here concerned—we are seeking to make clear an obvious distinction, namely, the distinction between knowledge by acquaintance and knowledge by description.

What kind of knowledge is it that we acquire by description? Knowledge about things with which we are not first acquainted. The most important knowledge that we possess or acquire is knowledge of objects which we know only by the knowledge we have about them—objects that we know about without knowing them. They are not direct impressions on our senses, nor are they ideas known in actual experience. We make judgments about them, and the subjects about which we make these judgments are really composed of these judgments that we make about them. To go back to our illustrations, we may know a great deal about the evil eye, a malignant influence, disease, faith, healing, causality, physical objects, without any acquaintance with them, without even knowing that they exist. Such knowledge is descriptive, and the objects are descriptions. Knowledge by description is never quite simple, and is often very complex, for, besides the relation of the mental act to the object known, there are the terms and relations which are the elements in the judgment and the relations of the judgments themselves. If we analyse a judgment, every word in which it is expressed, whether it is a noun or a verb or a preposition or a conjunction, conveys a distinct meaning, indicates a term or a relation, each of which can be made a distinct object to the mind, and all of which are combined in the single meaning the judgment expresses. It is in this complexity that the possibility of error lies, and the possibility increases as the complexity increases. All the terms and the relations which a judgment contains depend on the knowledge we have by acquaintance—that is to say, we are ultimately dependent on our actual experience for all knowledge whatever, whether it is acquaintance or description, for we can only describe in terms with which we are acquainted; but in the judgment these elements are combined into new objects, or a certain relation is declared to exist between objects, and it is this combination of the elements of the judgment that involves its truth or falsehood.

If this view of the nature of the mental act of knowing is accepted, we are able to understand how false opinion is consistent with the fact that all knowledge is truth. We escape both the alternatives that seemed to Socrates the only possible ones. "When a man has a false opinion, does he think that which he knows to be some other thing which he knows, and knowing both is he at the same time ignorant of both? Or does he think of something which he does not know as some other thing which he does not know?" No, neither; in error he thinks that something that he knows is in a relation that he knows to some other thing that he knows, when in fact that relation is not relating the two things. The false proposition is not one in which the constituent terms and relations are unknown or non-existent, but one in which a combination of these terms and relations is thought to exist when in fact it does not exist; and the true proposition is that in which the combination thought to exist does exist. We can, therefore, if this account be true, at least know what false opinion or error can be, whether or not we have any means of deciding in regard to any particular opinion that it is false.

There is one other theory, the last we shall notice. It is in one respect the most important of all, namely, that it is the most direct attempt to grapple with the problem of error. It is founded on a theory of knowledge which we owe mainly to the profound and acute work of a German philosopher (Meinong), and which at the present time is being keenly discussed. It is an attempt to determine more exactly than has yet been done the fundamental scheme of the mental life and development. The brief account that I am now offering, I owe to a paper by Prof. G. F. Stout on "Some Fundamental Points in the Theory of Knowledge." We have seen that the problem of error is the difficulty there is in conceiving how there can be any real thing, any real object of thought, intermediate between being and not-being. Error seems to exist and yet to have a nature which is a negation of existence, and it seems therefore to be a downright contradiction when we affirm that error or false opinion can be—that there is a real object of thought when we judge falsely. This theory meets the difficulty directly by distinguishing in the mental act of knowing a process that is neither perceiving nor thinking of things, and that involves neither believing nor disbelieving on the one hand nor desiring or willing on the other: this is the process of supposing. Corresponding to this mental act of supposing, there is a distinct kind of object intended or meant by the mind—an object that is neither a sense datum nor an idea, nor a judgment, but a supposition. Also and again corresponding to this mental act of supposing and its intended object the supposition, there is a mode of being which is neither existence nor non-existence, but is named subsistence. A supposition, it is said, does not exist—it subsists. This thesis, it will easily be understood, is based on an analysis, and deals with arguments that touch the most fundamental problems of theory of knowledge. Moreover, its presentment is excessively technical, and only those highly trained in the habit of psychological introspection and skilled in philosophical analysis are really competent to discuss it. It is not possible to offer here anything but a simple outline of the part of the theory that concerns the present problem. The actual experience of knowing is a relation between two things, one of which is a mental act, the act of perceiving or thinking or having ideas, and the other is an object, that which is perceived or thought of. The act is a particular mental existence, it is the act of a psychical individual. The object is not included within the actual experience which is the knowing of it, it is that which is meant or intended by the experience. The act, then, is the mental process of meaning or intending, the object the thing meant or intended. The mental act differs according to the kind of object intended. The act of perceiving is the direction of the mind towards sense data and ideas; the act of judging is the direction of the mind towards judgments or propositions about things, propositions that affirm or deny relations between things; the act of supposing is different from both these—it is the direction of the mind towards suppositions. Suppositions differ from ideas in this, that they may be either positive or negative, whereas ideas are never negative. This may seem to contradict experience. Can we not, for example, have an idea of not-red just as well as an idea of red? No, the two ideas can easily be seen to be one and the same; in each case it is red we are actually acquainted with, and the difference is in affirming or denying existence to the one idea. The difference is in our judgment, which may be affirmative or negative. A supposition is like a judgment in this respect; it may be either affirmative or negative, but it differs from a judgment in another respect, that while a judgment always conveys a conviction, always expresses belief or disbelief, a supposition does not—it is neither believed nor disbelieved.

Before I show the application of this analysis of knowledge to the problem of error, let me try and clear up its obscurity, for undoubtedly it is difficult to comprehend. Its difficulty lies in this, that though all the ideas with which it deals are quite familiar—suppositions, real and unreal possibilities, fulfilled and non-fulfilled beliefs—yet it seems to run counter to all our notions of the extreme simplicity of the appeal to reality. It seems strange and paradoxical to our ordinary habit of thinking to affirm that there are real things and real relations between things which though real yet do not exist, and also that non-existent realities are not things that once were real but now are nought—they are things that subsist. Yet this is no new doctrine. The most familiar case of such realities is that of numbers. The Greeks discovered that numbers do not exist—that is to say, that their reality is of another kind to that which we denote by existence. Numbers are realities, otherwise there would be no science of mathematics. Pythagoras (about 540-500 B.C.) taught that numbers are the reality from which all else is derived. And there are many other things of the mind that seem indeed to be more real than the things of sense. It is this very problem of error that brings into relief this most important doctrine.

Now let us apply this theory of the supposition to the problem of error, and we shall then see how there can be an object present to the mind when we judge falsely, and also that the object is the same whether we judge truly or falsely. Suppositions are real possibilities; they are alternatives that may be fulfilled or that may never be fulfilled. These real possibilities, or these possible alternatives, are objects of thought; they do not belong to the mental act of thinking; they are not in the mind, but realities present to the mind. In mere supposing they are present as alternatives; in judging, we affirm of them or deny of them the relation to general reality that they are fulfilled. Judgments therefore are true or false accordingly as the fulfilment they affirm does or does not agree with reality. In this way, then, we may answer the perplexing question, How can there be an object of thought in a false judgment? The answer is, that the objects of thought about which we make judgments are suppositions, and our judgments concern their fulfilment, and their fulfilment is a relation external to them—it is their agreement or disagreement with reality.