PART III.

THE PRINCIPLES OF REASONING-(continued.)

WE have now gone through the second part of our book. In the first, you will recollect, we considered the Introduction to Reasoning. In the second part, we considered the Principles of Reasoning. In this part, we are going to consider still further the principles of reasoning. But these principles are of a different kind. In the former part the principles had a direct relation to the subject itself; we took the subject, and considered its attributes, its parts, its kinds, its causes, and its effects. In this part we shall consider the subject in its relation to other things. You may therefore, if you please, call the principles we have discussed, the internal principles of reasoning; and those we are going to discuss, the external principles of reasoning. These we shall consider in separate sections, under the following heads:-Section 1. Reasoning from Examples. 2. Reasoning from Analogy, Comparison, and Contrast. 3. Reasoning from Parables, Fables, and Proverbs. 4. Reasoning from Written Documents. 5. Errors in Reasoning.

SECTION I.

REASONING FROM EXAMPLES.

IN reasoning from examples we adduce examples in proof of the propositions we desire to establish.

1. The following are instances:

"And it came to pass, that he went through the corn fields on the sabbath day; and his disciples began, as they went, to pluck the ears of corn. And the Pharisees said unto him, Behold, why do they on the sabbath day that which is not lawful? And he

said unto them, Have ye never read what David did, when he had need, and was an hungred, he, and they that were with him? How he went into the house of God in the days of Abiathar the high priest, and did eat the shewbread, which is not lawful to eat but for the priests, and gave also to them which were with him? And he said unto them, The sabbath was made for man, and not man for the sabbath: therefore the Son of man is Lord also of the sabbath."-Mark ii. 23-28.

"It would be an extremely profitable thing to draw up a short and well-authenticated account of the habits of study of the most celebrated writers with whose style of literary industry we happen to be most acquainted. It would go very far to destroy the absurd and pernicious association of genius and idleness, by showing them that the greatest poets, orators, statesmen, and historians,men of the most brilliant and imposing talents,have actually laboured as hard as the makers of dictionaries and the arrangers of indexes; and that the most obvious reason why they have been superior to other men is, that they have taken more pains than other men. Gibbon was in his study every morning, winter and summer, at six o'clock; Mr. Burke was the most laborious and indefatigable of human beings; Leibnitz was never out of his library; Pascal killed himself by study; Cicero narrowly escaped death by the same cause; Milton was at his books with as much regularity as a merchant or an attorney,--he had mastered all the knowledge of his time; so had Homer. Raffaelle lived but thirty-seven years; and in that short space carried the art so far beyond what it had before reached, that he appears to stand alone as a model to his successors. There are instances to the contrary; but, generally speaking, the life of all truly great men has been a life of intense and incessant labour."-Rev. Sydney Smith's Moral Philosophy.

"If then we consider the perpetual conflicts of savage tribes, the frequent wars of the rival republics of Greece with each other, and with their common enemies; if we remember that the temple of Janus at Rome, always open in the time of war, was never closed during five centuries, till the end of the second Punic war, and then only for a short time; if we advert to the desolation caused by the Scythians, Goths, Vandals, Tartars, and the destruction of about two millions of human beings in the Crusades, it seems to be evident that wars were anciently, and before the general use of firearms and cannon, more frequent, protracted, destructive, and cruel than they are now."—Aiken on War.

"Yes, sir, if ever you was to Antwerp, you'd see what it is to lose colonies. When that place belonged to Holland, and had colonial trade, five thousand marchants used to meet on 'Change;

now the Exchange is left, but the marchant is gone. Look at the great docks built there, at so much expense, and no shipping there. Look at one man-of-war for a navy that has a pennant as long as from to-day to the middle of next week, that can't get out for the Dutch forts, is of no use in, and if it did get out has no place to go to. Buonaparte said he wanted ships, colonies, and commerce; Buonaparte was a fool, and didn't know what he was a-talkin' about, for colonies means all three."-Sam Slick.

2. This mode of reasoning from examples is called by scholastic logicians induction, and is opposed to deduction. We will, then, illustrate the difference between reasoning by induction and reasoning by deduction. You have observed an individual come to poverty by a dishonest course of action, and another arrive at wealth by a life of rectitude; and you remark, "Honesty is the best policy. Here you reason by induction. From these individual cases you gather a proof of the general maxim, " Honesty is the best policy." But suppose a person should ask your advice how to act in a case wherein strict integrity might appear to be less advantageous than a more crooked procedure, and you observe to him, "Honesty is the best policy" here you reason by deduction. You apply the general principle to an individual case; you reason on the principle of genus and species. These two kinds of reasoning are just the reverse of each other. When from one or more examples you infer a general principle, that is called induction, or reasoning from examples. When from the general principle you infer an individual case, that is called deduction, or reasoning from genus and species. Induction is reasoning from particulars to generals, and deduction is reasoning from generals to particulars.

But you ask, How can I infer a general proposition from a small number of examples? Is it not a rule, that generals cannot be inferred from particulars?" Very true. You cannot infer generals from particulars, unless you have reason to believe that all the particulars are alike. Our reasoning here must depend upon the uniformity of the laws of nature. When the law is uniform, we can infer generals from particulars, because we know that all particulars are in fact generals. This is the case most frequently in the physical sciences.

All animals of

:

the same species are alike. I see that a horse has four legs I may assert then that every horse in the world has four legs, though I have not seen them all. I decompose a glass of water, and find it is formed of oxygen and hydrogen: I therefore assert that all water, everywhere, is composed of oxygen and hydrogen. But when this constant uniformity does not exist, I cannot reason so conclusively; and my reasonings will be weaker and weaker in proportion to this want of uniformity; and hence we shall have to descend from certain reasonings, to probable reasonings, and then lower, to doubtful reasonings, until at last our examples may be so few or so conflicting, that we may have no foundation for any reasoning at all respecting the matter in dispute.*

'Be not too hasty to erect general theories from a few peculiar observations, appearances, or experiments. This is what the logicians call a false induction. When general observations are drawn from so many particulars as to become certain and indubitable, these are jewels of knowledge, comprehending great treasure in a little room: but they are therefore to be made with the greater care and caution, lest errors become large and diffusive, if we should mistake in these general notions."-Watts on the Improvement of the Mind.

Some writers make a distinction between reasoning from example and reasoning from induction,—the example is one, induction is more than one. But there seems no ground for this distinction. The mode of reasoning is the same; the only difference is in the degree of proof. The greater the number of examples, of course, the greater is the amount of evidence in proof of the general proposition.†

In reasoning then from genus and species, we infer, you perceive, individual cases from universal rules. In reasoning from examples, we reverse our mode of reasoning; and from one or more examples we prove the general rule.

* "When the grounds for believing anything are slight, we term the mental act or state induced, a conjecture; when they are strong, we term it an inference or conclusion. Increase the evidence for a conjecture, it becomes a conclusion; diminish the evidence for a conclusion, it passes into a conjecture. The process which ends in a conclusion, and the process which ends in a conjecture, are thus essentially the same, and differ only in degree, or in the force of the evidence."Bailey, p. 31.

It is obvious that whether we can draw an inference from a single fact, or whether it is needful to have a collection of facts, depends altogether on what is requisite for establishing a similarity in the influential circumstances of each case, and does not affect the character of the reasoning."-Bailey, p. 10.

We use the inductive method in regard to the physical sciences, such as astronomy, chemistry, &c. We see several instances in which fire melts lead; we infer it will always do so; and when we are satisfied that this is the case, we call it a law of nature. It was also by this method that philosophers have discovered the laws of astronomy. By the same rule we discover the laws of medicine if a medicine cures in a great number of cases, we infer that it will always cure in similar cases. In the science of morals, we also observe that certain vices lead to misery; and we infer that vice will always lead to misery, and virtue to happiness. In politics, we observe in the history of the world what institutions and what laws have conduced to the happiness of the people; we gather together these instances, and thus form maxims for the government of nations. In political economy we observe, or should observe, the same practice. But political economists have too often wandered into other paths. Instead of deducing their principles from facts, they have first formed their theories, and then made facts bend to their theories. Hence we have theories of population, theories of rent, theories of the currency, and theories of taxation, advanced and supported in a way more in accordance with the Aristotelian than with the Baconian system of philosophy.

3. The following explanation of the nature of induction is taken from Mr. Hill's Logic:

"An induction in which every individual case is enumerated is a perfect demonstration. And in general, the more nearly we approach to the entire enumeration, the higher is the degree of probability attained by the induction: provided, at least, that no facts of an opposite tendency are discoverable; or that if they occur, they are satisfactorily shown not to be really inconsistent with the principle deduced. The great error in induction is too great haste in drawing a conclusion without having premised a sufficient number of individual cases. Many, for example, if they have met with or heard of one or two dishonest lawyers, or observed a comet in a warm summer, think themselves authorized to draw the sweeping inference, that all lawyers are dishonest, or all comets occasion a warm season. ""

"A beautiful specimen of moral induction occurs, 2 Peter ii. 4-9. The conclusion is two-fold; and the sacred writer accord