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SOURCES OF ERROR.

177. I. Prejudice. The first source of error is Prejudice, which at the outset substitutes desire for reason.

178. II. Mal-Observation. Non-Observation. We may observe carelessly or omit observing.

179. III. False Generalization, or Induction. While we are proceeding from the observation of individuals to a statement about a class or genus, we are liable to error. The most obvious error is to make the general statement, or generalize, as it is called, from insufficient observation. Thus a child might infer that all men are kind from the single instance of his father, cr, from more numerous but still insufficient instances, that all men are white.

180. IV. Confusion.

Sometimes, when we are deduc

ing a statement from two other statements, we may (1) confuse the meaning of the words, or (2) we may not understand what statement is intended to be deduced. Thus (1): –

An effective speaker persuades his audience;
He always speaks effectively;

Therefore he always persuades his audience.

Here is a confusion between "effective" in the second statement, used rightly in the sense of "calculated to be effectual," and effective in the first statement, wrongly used for "effectual." Another very common error is to use a verb, in one of the premises, with an implied qualification of "generally," and then, in the conclusion, to use the verb without that qualification, or even to insert "always."

Thus :

A skilful speaker (generally) persuades his audience;
He is a skilful speaker;

Therefore he always persuades his audience.

Such errors are called " errors of confusion." Examples of (2) are not uncommon: a juror may think that a man is proved to be a thief because he is proved to be a vagrant; or a barrister may prove that a man is a very amusing rogue, when the real thing to be proved is that the man is not a rogue at all; and he may confuse a jury into fancying that he has proved the latter, when he has only proved the former.

Even

181. V. False Ratiocination, or Deduction. though the two statements from which we deduce a conclusion are correct and clearly understood, yet in the process of deduction we are liable to mistakes which will be described hereafter. One example will suffice for the present:·

All Englishmen like roast beef;

I like roast beef;

Therefore I am an Englishman.

HOW TO AVOID ERROR.

There is

182. Personal Observation and Prejudice. nothing which seems to us so certain as that which we have ourselves seen, heard, or otherwise perceived by our senses. And we may say with truth, strictly speaking, that our senses never deceive us.1 But it is very difficult to distinguish the

1 It is not intended here to touch on the subject of so-called optical delusions, and other results of an excited imagination. Even in such

evidence of our senses from the inferences which we draw from that evidence; and these inferences are often mistaken. Even in such a statement as "I am happy," an inference is implied that the state of the speaker resembles a state of which the speaker has often heard, called "happiness." The inference may be wrong, and the speaker ought perhaps to have said, "I am merry," or "I am contented." Such mistakes as these are common with children and foreigners, and they can only be avoided by experience and observation. But they would generally be treated as mistakes in the use of language, and would not come within the province of Logic.

says,

"The

A different kind of mistake occurs when a child sun moves," and, on being told that he is wrong, replies, “I see it move." The child does not see the sun move; he only sees the sun changing its place relatively to trees, houses, and hills, all of which appear to remain fixed, and he thence infers that the sun moves. In the same way, a grown-up man might assert that on some misty day he had seen the sun rise some seconds before the time set down in the calendar; whereas he had merely seen an image of the sun raised to an unusual degree above the horizon by excessive refraction. These are mistaken inferences. In saying "I am happy," the meaning of the speaker was correct, but his words did not express his meaning. In saying "The sun moves," the speaker expresses his meaning, but his meaning is wrong.

Beside the natural tendency to draw hasty inferences of any kind, we are also tempted to force our inferences from

cases it may fairly be said that the person who sees the sight is right in saying that he sees it, and only wrong in inferring that others must see it, or that he can touch what he sees.

observation to correspond with our prejudices or misconceptions. Thus a timid child, who is predisposed to see fearful sights by night, mistakes a bush or post for a ghost or a robber; a person who has been told of "the man-in-the-moon " finds it easy to trace in the moon the features of a man.1 Such prejudices have often seriously retarded the progress of science by preventing careful observation. Thus it was long thought that, the circle being a perfectly symmetrical figure, the heavenly bodies must move in circles; the earth, being superior in dignity to the sun, could not move round the sun; a weight ten times as heavy as another must fall ten times as fast; the magnet must exercise an irresistible force, etc. It is said that even now the negroes affirm that the color of the coral which they wear as an amulet is affected by the health of the wearer.

Authority frequently originates and supports prejudice. Thus for many years it was affirmed on the authority of Galen that there was a communication between the two sides of the heart. Men dissected and examined, and remarked that the communication was hard to see; but they were prevented by prejudice from seeing that there was no communication at all.

Another fertile source of prejudice is a false belief that whatever causes phenomena must resemble the phenomena, and vice versa. Hence it was thought that the planet Mars, being red, like blood, caused bloodshed; that the elixir vitæ, being precious, must be some mixture containing potable gold, the most precious of all metals; that the lungs of the

1 Or in the night, imagining some fear,
How easy is a bush supposed a bear!

Midsummer-Night's Dream.

fox, a long-winded animal, were a specific against asthma, etc.1 It follows that, if we desire to attain to the truth, we must, before and whilst observing, keep our minds clear from prejudice.

183. Induction by Enumeration. - The Induction which proceeds from the mere enumeration of instances to a general statement about a class as, for example, from "all the horses that I have seen or heard of have had four legs," to "all horses have four legs" — is evidently an insecure method of proof. It is based upon the principle of the uniformity of Nature, "what has been is and will be." We may think it absurd to suppose that a horse could have six legs. But so it might have seemed absurd some centuries ago to a negro in the heart of Africa to doubt that "all men are black," or to a North American Indian to doubt that "all men are red," or to a Malay to doubt that "all men are yellow."

184. Induction is always incomplete. When a negro who had been in the habit of maintaining that “all men are black" met a white or red man, he would have two courses open to him. He could either say that the white was not a man, or he could give up his old definition of man, and make a new one. Thus all statements that result from merely enumerative induction are temporary and liable to correction. They may therefore be called provisional. Sometimes the instances enumerated may be ludicrously insufficient, as if a child of a soldier in the Scots Grays should infer from induc

1 The fat of an adder was once thought to be an antidote against the effects of its bite. Compare the proverb about "a hair of the dog that bit you."

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