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including imperfect induction, is both a legitimate and a valuable means for the extension of knowledge. It is more than that. According to some philosophers it is the only process of reasoning that furnishes us with knowledge at all, and all our knowledge is ultimately due to it.

When the investigation that precedes inductive inference, whether in the world of matter or in the world of thought, is given in detail together with the results and the inferred generalizations, we have one kind of argumentation. Such is our object here: to draw from an array of particular facts a general law or truth, and to present the whole in as convincing a form as may be.

The greatest work that has yet been done in the field of modern science owes its value to the long and patient investigation of facts which preceded every theory the investigator ventured to propound. Note what Darwin says in the introduction to his Origin of Species:

When on board H. M. S. "Beagle," as naturalist, I was much struck with certain facts in the distribution of the organic beings inhabiting South America, and in the geological relations of the present to the past inhabitants of that continent. These facts, as

will be seen in the latter chapters of this volume, seemed to throw some light on the origin of species-that mystery of mysteries, as it has been called by one of our greatest philosophers. On my return home, it occurred to me, in 1837, that something might perhaps be made out on this question by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing on it. After five years' work I allowed myself to speculate on the subject, and drew up some short notes; these I enlarged in 1844 into a sketch of the conclusions, which then seemed to me probable from that period to the present day I have steadily pursued the same object. I hope that I may be excused for entering on these personal details, as I have given them to show that I have not been hasty in coming to a decision.

As an example of the investigator's methods, bearing on one of the subjects given above, read the following from the same book:

I am tempted to give one more instance showing how plants and animals, remote in the scale of nature, are bound together by a web of complex relations. I shall hereafter have occasion to show that the exotic Lobelia fulgens is never visited in my garden by insects, and consequently, from its peculiar structure, never sets a seed. Nearly all our orchidaceous plants absolutely require the visits of insects to remove their pollen-masses and thus to fertilize them. I find from experiment that humble-bees are almost indispensable to the fertilization of the heartsease (Viola tricolor), for other bees do not visit this flower. I have also found that the visits of bees are necessary for the fertilization of some kinds of clover for instance, 20 heads of Dutch clover (Trifolium repens) yielded 2290 seeds, but 20 other heads protected from bees produced not one. Again, 100 heads of red clover (T. pratense) produced 2700 seeds, but the same number of protected heads produced not a single seed. Humble-bees alone visit red clover, as other bees cannot reach the nectar. It has been suggested that moths may fertilize the clovers; but I doubt whether they could do so in the case of the red clover, from their weight not being sufficient to depress the wing-petals. Hence we may infer as highly probable that, if the whole genus of humble-bees became extinct or very rare in England, the heartsease and red clover would become very rare, or wholly disappear. The number of humble-bees in any district depends in a great measure on the number of fieldmice, which destroy their combs and nests; and Col. Newman, who has long attended to the habits of humble-bees, believes that "more than two-thirds of them are thus destroyed all over England." Now the number of mice is largely dependent, as every one knows, on the number of cats; and Col. Newman says, "Near villages and small towns I have found the nests of humble-bees more numerous than elsewhere, which I attribute to the number of cats that destroy the mice." Hence it is quite credible that the presence of a feline animal in large numbers in a district might

determine, through the intervention first of mice and then of bees, the frequency of certain flowers in that district !

A few lines, further on, will give a hint of work still to be done in a direction in which the student may get interesting results well worth recording :

The difference in the length of the corolla in the two kinds of clover, which determines the visits of the hive-bee, must be very trifling; for I have been assured that when red clover has been mown, the flowers of the second crop are somewhat smaller, and that these are visited by many hive-bees. I do not know whether this statement is accurate; nor whether another published statement can be trusted, namely, that the Ligurian bee, which is generally considered a mere variety of the common hive-bee, and which freely crosses with it, is able to reach and suck the nectar of the red clover.

In the treatment of the first subject given above, make a record of your dreams, tracing everything in them as far as possible to some experience or impression of waking life. Appeal also to the experience of your friends.

EXERCISE L.

DEDUCTIVE REASONING.

Subjects:

Shakespeare the Product of His Age.

An Early Change in the Government of Russia Inevitable.
Reasons why Human Slavery should not be Tolerated.
The Successful Man.

John Brown, Hero.

There is a process of reasoning just the reverse of that with which we have been dealing. Given the

general law for a class of objects or instances, we can proceed to apply it to any particular object or instance in the class. If all men are mortal, one man is mortal, and if I am a man I am mortal. If copper is a conductor of electricity and if lightning is electricity, then copper is a conductor of lightning. These are examples of deduction. Let us put them in the form of what is known in logic as a syllogism:

Major premise: All men are mortal.
Minor premise: James is a man.

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Electricity is conductible by copper.

Lightning is electricity.

Therefore, lightning is conductible by copper.

It must be at once evident to all that these conclusions are indisputably correct- that is, if the premises are. The deductive process in itself is not open to the objection which the inductive process is open to, for it does not go beyond the limits with which it begins. But there may be some question in regard to those limits. We must have premises in order to draw a conclusion. Those premises are established by induction; if by imperfect induction, there is a possibility of their being untrue; and if they are not true the conclusion itself may be false. Thus, by observing the satellites of Jupiter, Saturn, and the Earth, astronomers had at one time concluded that the satellites of our planetary system revolve from west to east. They could therefore very well infer that if Uranus was attended by any satellites they revolved from west to east. Uranus is attended by a number of satellites, but they revolve from east to west. The induction

had been imperfect, and as it happens, incorrect; and the inference, though drawn by a correct process, was also incorrect.

The danger from this source is twofold. Not only may the one premise which asserts a general truth of a class be false, but the other which assigns an individual to that class may also be false. Suppose we say: All poison-oak is an oak;

oaks have simple leaves; the therefore the poison-oak has simple leaves. Our conclusion is false, not because the deductive process of reasoning is fallacious but because the second premise is fallacious: the poison-oak is not a member of the oak-family at all.

Of course we go on making deductive inferences, and trusting them too. If now and then one turns out to be wrong we go back and examine our premises, and if we discover a false induction, that is so much gained; the discovery of an error always brings us so much nearer the truth.

The great body of argumentative literature is founded upon deductive reasoning. Rarely however in composition do we employ anything so formal as the complete syllogism. Here is one example from Matthew Arnold: "Genius is mainly an affair of energy, and poetry is mainly an affair of genius; therefore, a nation whose spirit is characterized by energy may well be eminent in poetry." But nearly always one of the premises is unexpressed; sometimes the inference itself is not drawn. When we say, When we say, "The treatise will not be popular because it is so abstract," we trust to everybody to supply the premise, "Abstract treatises are not popular."

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