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Why describe Logic as a system of defence against error? Why say that its main end and aim is the organisation of reason against confusion and falsehood? Why not rather say, as is now usual, that its end is the attainment of truth? Does this not come to the same thing?

Substantially, the meaning is the same, but the latter expression is more misleading. To speak of Logic as a body of rules for the investigation of truth has misled people into supposing that Logic claims to be an art of Discovery, that it claims to lay down rules by simply observing which investigators may infallibly arrive at new truths. Now, this does not hold even of the Logic of Induction, still less of the older Logic, the precise relation of which to truth will become apparent as we proceed. It is only by keeping men from going astray and by disabusing them when they think they have reached their destination that Logic helps men on the road to truth. Truth often lies hid in the centre of a maze, and logical rules only help the searcher onwards by giving him warning when he is on the wrong track and must try another. It is the searcher's own impulse that carries him forward: Logic does not so much beckon him on to the right path as beckon him back from the wrong. In laying down the conditions of correct interpretation, of valid argument, of trustworthy evidence, of satisfactory explanation, Logic shows the inquirer how to test and purge his conclusions, not how to reach them.

To discuss, as is sometimes done, whether Fallacies lie within the proper sphere of Logic, is to obscure the real connexion between Fallacies and Logic. It is the existence of Fallacies that calls Logic into existence; as a practical science Logic is needed as a protection against Fallacies. Such historically is its origin. We may, if we like, lay down an arbitrary rule that a treatise on Logic should be content to expound the correct forms of interpretation and reasoning and should not concern itself with the wrong. If we take this view we are bound to pronounce Fallacies extra-logical. But to do so is simply to cripple the usefulness of Logic as a practical science. The manipulation of the bare logical forms, without reference to fallacious departures from them, is no better than a nursery exercise. Every correct form in Logic is laid down as a safeguard against some erroneous form to which men are prone, whether in the interpretation of argument or the interpretation of experience, and the statement and illustration of the typical forms of wrong procedure should accompany pari passu the exposition of the right procedure.

In accordance with this principle, I shall deal with special fallacies, special snares or pitfalls—misapprehension of words, misinterpretation of propositions, misunderstanding of arguments, misconstruction of facts, evidences, or signs—each in connexion with its appropriate safeguard. This seems to me the most profitable method. But at this stage, it may be worth while, by way of emphasising the need for Logic as a science of rational belief, to take a survey of the most general tendencies to irrational belief, the chief kinds of illusion or bias that are rooted in the human constitution. We shall then better appreciate the magnitude of the task that Logic attempts in seeking to protect reason against its own fallibility and the pressure of the various forces that would usurp its place.

It is a common notion that we need Logic to protect us against the arts of the Sophist, the dishonest juggler with words and specious facts. But in truth the Inner Sophist, whose instruments are our own inborn propensities to error, is a much more dangerous enemy. For once that we are the victims of designing Sophists, we are nine times the victims of our own irrational impulses and prejudices. Men generally deceive themselves before they deceive others.

Francis Bacon drew attention to these inner perverting influences, these universal sources of erroneous belief, in his De Augmentis and again in his Novum Organum, under the designation of Idola, (εἴδωλα) deceptive appearances of truth, illusions. His classification of Idola—Idola Tribus, illusions common to all men, illusions of the race; Idola Specus, personal illusions, illusions peculiar to the "den" in which each man lives; Idola Fori, illusions of conversation, vulgar prejudices embodied in words; Idola Theatri, illusions of illustrious doctrine, illusions imposed by the dazzling authority of great names—is defective as a classification inasmuch as the first class includes all the others, but like all his writings it is full of sagacious remarks and happy examples. Not for the sake of novelty, but because it is well that matters so important should be presented from more than one point of view, I shall follow a division adapted from the more scientific, if less picturesque, arrangement of Professor Bain, in his chapter on the Fallacious Tendencies of the Human Mind.¹

The illusions to which we are all subject may best be classified according to their origin in the depths of our nature. Let us try to realise how illusory beliefs arise.

What is a belief? One of the uses of Logic is to set us thinking about such simple terms. An exhaustive analysis and definition of belief is one of the most difficult of psychological problems. We cannot enter upon that: let us be content with a few simple characters of belief.

First, then, belief is a state of mind. Second, this state of mind is outward-pointing: it has a reference beyond itself, a reference to the order of things outside us. In believing, we hold that the world as it is, has been, or will be, corresponds to our conceptions of it. Third, belief is the guide of action: it is in accordance with what we believe that we direct our activities. If we want to know what a man really believes, we look at his action. This at least is the clue to what he believes at the moment. "I cannot," a great orator once said, "read the minds of men." This was received with ironical cheers. "No," he retorted, "but I can construe their acts." Promoters of companies are expected to invest their own money as a guarantee of good faith. If a man says he believes the world is coming to an end in a year, and takes a lease of a house for fifteen years, we conclude that his belief is not of the highest degree of strength.

The close connexion of belief with our activities, enables us to understand how illusions, false conceptions of reality, arise. The illusions of Feeling and the illusions of Custom are well understood, but other sources of illusion, which may be designated Impatient Impulse and Happy Exercise, are less generally recognised. An example or two will show what is meant. We cannot understand the strength of these perverting influences till we realise them in our own case. We detect them quickly enough in others. Seeing that in common speech the word illusion implies a degree of error amounting almost to insanity, and the illusions we speak of are such as no man is ever quite free from, it is perhaps less startling to use the word bias.