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In all attempts to convince the judgment of those addressed there are processes of reasoning which may be termed general and specific.
1. General Classification. It is found that all forms of reasoning fall under one or the other of two general types:
(1) Inductive method. When a general conclusion is drawn from particular instances, the reasoning is inductive. An induction is, therefore, proof based upon certain related particulars, or as Bautain says, it is the drop of oil extracted from thousands of roses; the healing power of a hundred-weight of bark in a few grains of quinine." Thus, the men A, B, C, &c. die; therefore all the men will. die. The inductive is a natural and an extremely easy method of reasoning; the most ordinary people practise it. Sir John Herschel, therefore, speaks of "the impulse of the human mind to generalize," and of the inductive propensity." The impor
tance, too, of this method cannot be overestimated. It is found necessary, as Locke remarks, for the
mind "to shorten its way to knowledge and make each perception more comprehensive by binding them in bundles."
The following principles should be observed while reasoning inductively:
a. The exclusion of important particulars and the introduction of unimportant ones will probably lead to false inductions.
b. The repetition of the same kind of particulars does not fortify the argument. Tutor "What can you say of the second law of thought?" Student "It cannot both be and not be. For ex
ample, the door over there must be either shut or
take the case of another door."
c. Reliance upon a limited number of particulars when an ample number is at command, is unphilosophical.
d. Hasty inductions built upon limited particulars may seem to prove anything. It has thus been proved, at least to the satisfaction of many, that the earth is both a flat surface and a sphere; that ministerial education is both beneficial and injurious. If the preacher hastily forms his Biblical theology from a few isolated passages, his doctrines most likely will be worthless and erroneous. Hasty inductions have killed many a patient, and lost many a case at the bar. It is clear, therefore, that the investigator and reasoner should spare no pains in collecting the facts and data upon which he is to
make his induction. Professor Swing has thus happily expressed the importance of broadness in our observations: "As we cannot take up a drop of water from the Atlantic and find in that drop the flow of the tides, the lifting up of the billows, the power that floats all the ships of a thousand ports, and the soft and loud music of a calm and storm; as to see the ocean we must grasp in all its rocky bed bordered by continents, so we cannot in the face of a dying infant, or the adversity of a good man, see the government of the love of God. It has boundaries wider than these. We must wait, and what the fleeting moments of man deny, ask the great years of God to bring. The tides of the mind, the deep music of human waters, cannot be seen in the drop of life."
e. The number of instances from which the induction is made must be increased in proportion both to the irregularity of the instances, and to the difficulties attending the proposition to be established.
f. Inanimate nature, owing to its greater uniformity, requires of particular cases upon which to make a correct induction, a smaller number than does animate nature, and for the same reason brute nature requires a smaller number than human
g. When all the data at command are viewed, an inference will result; but the mind must hold itself in readiness to yield that inference for another upon the arrival of additional data. Some one blamed Dr. Marsh for changing his mind. "Well," he
replied, "that is the difference between a man and a jackass; the jackass can't change his mind and the man can it's a humar privilege."
h. In debate the burden of proof rests upon the one whose induction has the weakest support; the burden of proof is, therefore, shifted when that induction is sufficiently strengthened by additional data.
i. An absolutely unquestionable induction can be reached only when all the data belonging to a given class are taken into account; it follows, therefore, that an absolutely unquestionable induction is a demonstration or a fact. For illustration, "all men are mortal," because as far as our experience goes, and from the uniformity of the laws of nature, we are confident that they will always prove to be so. But from the nature of the case, the mortality of man can never be universally established till the end of time. Hence most of our general principles, which rest upon induction, are, strictly speaking, but probable truths.
(2) The deductive method. A general conclusion having been reached, the application of it to some particular instance, is reasoning by the process of deduction. A deduction is, therefore, proof based upon some general law. Thus, all men die, therefore we shall die. Of the two processes, the inductive and deductive, Sir W. Hamilton, in Philosophical Discussions, thus remarks: "The former is governed by the rule,- What belongs (or does not belong) to all the constituent parts, belongs
(or does not belong) to the constituted whole. The latter by the rule,- What belongs (or does not belong) to the containing whole, belongs (or does not belong) to each and all of the contained parts." 50
It is evident, if the facts at command are numerous, that the inductive naturally precedes the deductive method; that is, the law must be inferred from the collected particulars before it can be applied to some given particular. This is the basis of Horne Tooke's remark: "Reasoning is only. addition and subtraction."
The preacher, basing his reasoning upon the facts of Revelation, is, at the outset, in possession of a general law (the text); his method, therefore, is deductive. He announces the law, perhaps pauses for a moment, to show its reasonableness, and then makes the application. This practice is so uniform in the pulpit that it leads to the rule that a preacher should employ the inductive method only when he intends to supplement it by the deductive. It is often the same with the lawyer before the court, and the physician while administering to his patient.
It may be further remarked, that when the inductive can be supplemented by the deductive method, the conclusion becomes a moral certainty. Thus, induction based upon several scientific facts rendered it probable that the diamond and charcoal were the same chemical substance. But if so, the inference followed that the diamond would burn. Deduction, therefore, applied the law that carbon burns to the