The student must be constantly on guard against this loose method of inductive reasoning. It is most prolific in indefinite and loosely stated conclusions seeking to masquerade under an appearance of validity. He should always examine his own conclusions as well as those of his opponent for the purpose of finding out whether the instances used to support them are merely the result of chance or coincidence. Let us suppose that the decrease observed in the three states named above has suggested the probability of the truth of one of the conclusions. The investigator should at once pick out a few of the most prominent manufacturing states and find statistics showing manufacturing values in them. For example, he might consult Massachusetts, Pennsylvania, Ohio, Michigan, Illinois, and Wisconsin. If the same decrease is found to have existed in these states the truth of the inductive conclusion becomes much more probable and at the same time the probability of coincidence becomes correspondingly less. The student, however, should continue his investigations and examine the statistics regarding all the manufacturing states of the Union. He should then frame his conclusion in such a way that it will stand supported by the evidence of all the specific instances.
B. The class of persons, events, or things about which the induction is made must be reasonably homogeneous.
After we have seen three or four elephants we feel pretty safe in saying that all elephants have trunks. After we have seen three or four red schoolhouses we do not feel safe in saying that all schoolhouses are red. The first class of objects is homogeneous, the second is not. Therefore we may safely generalize regarding the appearance and characteristics of all elephants from the three or four specimens which have come beneath our notice. As a class they possess in a marked degree common traits of character and appearance. No one member of the species is radically different from any other member. With schoolhouses, however, the situation is quite different. All schoolhouses in a given community may be built alike and the first three or four seen by an individual might be painted red; but since the class of schoolhouses is not homogeneous, he cannot therefore correctly arrive at the imperfect inductive conclusion that all schoolhouses are red. This illustration should indicate to the student who would employ imperfect induction that it is necessary to be careful in drawing a broad conclusion covering a class of persons, events, or things whose members he does not know to be reasonably homogeneous with respect to the point about which he wishes to argue.
To advance a step further in the consideration of this requirement, we must remember that it applies only to the homogeneity of the particular characteristic of the class regarding which a conclusion is desired. For example, if it is desired to arrive at some conclusion regarding the color of all schoolhouses, the inductive process could not well be applied because the class is by no means homogeneous in regard to this particular characteristic. However, if it is desired to arrive at a conclusion regarding the use to which all schoolhouses are put the imperfect induction may safely be used because the class is reasonably homogeneous in this characteristic.
C. The specific instances cited in support of the conclusion must be fair examples.
In an imperfect inductive argument the instances upon which the conclusion is based must be fairly representative of the class of persons, events, or things which it includes. A debater in an interscholastic contest took three examples of cities having the commission plan of city government as a basis for his argument in support of the proposition that all American cities should adopt the commission form of city government. He began by showing that the three cities,—Galveston, Des Moines, and Grand Rapids, were fair examples of American cities. He showed that they did not represent the exceedingly large cities nor the exceedingly small cities but that they possessed the chief characteristics of both. He produced evidence to prove that they were directly representative of nine-tenths of the cities in America and that the principles of government which would work well in these three cities, taken as examples, would work equally well in any American city. He then showed that the commission plan of city government had worked well in the three examples which he had proved to be fairly representative of all American cities.
The greatest temptation to error is that of selecting examples or incidents which are most favorable to the debater’s contentions. Such action is a flagrant violation of the great principle which should govern all argumentative discourse—the principle that truth should stand supreme over all contentions. It is not only dishonest to select unfair examples, but it is disloyal to those who uphold the debater in his efforts to persuade. Never should an example be presented which possesses characteristics unusual to the class which it purports to represent. An earnest effort should always be made to obtain the fairest examples possible.
D. Careful investigation must disclose no exceptions.
A person should seldom rely upon his own uncontradicted experience to support an inductive conclusion. The small child concludes that all children have fathers and mothers because it has a father and mother. The tropical savage concludes that all parts of the earth are warm because the part in which he lives is warm. Similarly we find reasonable persons adopting like generalizations based upon their own uncontradicted experience. The business man denounces all public officials as dishonest because he has found that two or three are dishonest. The farmer denounces all lawyers as dishonest because one lawyer has treated him dishonestly. In each of these cases it is evident that a little careful investigation would disclose enough exceptions to overthrow the conclusion.
The debater should examine his own inductions as well as those of his opponent for the purpose of discovering possible exceptions. The man who declared that all trades-union men are anarchists would have found the exceptions to his rule so overwhelming as to make his conclusion appear ridiculous. The difficulty is that the abnormal and exceptional instances which we know loom so large in our minds that they become prejudices and crowd out calm reason. The few union men who have destroyed life and property should not be made the specific instances supporting an induction regarding the whole class of trades-union men. The few college men who drink, swear, and carouse should not be made the specific instances supporting an induction regarding the whole class of college men. Every induction should be examined carefully for the purpose of discovering exceptions.