To die; to sleep;
    No more; and by a sleep to say we end
    The heart-ache and the thousand natural shocks
    That flesh is heir to.  ’Tis a consummation
    Devoutly to be wish’d.  To die; to sleep;—­
    To sleep?  Perchance to dream!  Ay, there’s the rub;
    For in that sleep of death what dreams may come,
    When we have shuffl’d off this mortal coil,
    Must give us pause.

But, as in this case of Hamlet’s, poetical analogies will not bear much strain; the aspect in which the similarity holds is usually the only aspect the two cases have in common, and to take poetry as a precise formulation of fact is to sin against both humor and sound reasoning.

In daily life we are constantly reasoning by analogy.  If you argue that a certain man who has been successful at the head of a railroad will therefore make a good president for a college because that also is a complex institution, or that because self-government has worked well in a certain school it will probably work well in a college, or that because a friend has been cured of sleeplessness by taking a walk just before going to bed therefore everybody who sleeps badly can be cured in the same way,—­in all these cases you are reasoning by analogy.  In each case it will be noticed you would pass from a similarity which exists in a single case or in a small number of cases to the conclusion.  The reasoning is sound, however, only in so far as the similarity bears on the actual purpose in hand:  in the first example, if the success of the railroad president arises from the power of understanding men and of philosophic insight into large problems, the reasoning will probably be valid; in the last example, if applied to insomnia due to overwork, it might be bad.

In practical affairs it is easy to find examples of reasoning from analogy, especially in arguments of policy.  The first trial of city government by commission depended on such reasoning:  when Galveston, Texas, was devastated by a storm it was reasoned that in business matters a small body of picked men with absolute powers are most efficient in an emergency, and that since the reconstruction of the city was essentially a matter of business, such a body would best meet the emergency.  So the extension of commission government in other states at first followed reasoning by analogy:  government by commission worked well in Galveston; it would probably work well in Des Moines.  In the same way with the arguments for a parcels post:  they proceed from the analogy of the present postal service, which has been successful so far as it goes, and from the success of the parcels post in almost all the countries of Europe.  If you were arguing that “Association” (or “soccer”) football should be made one of the major sports at your college, you would reason from the analogy of its great popularity with Englishmen all over the world that it would also probably be popular in America.