In such a subject our theory, instead of being an all-sufficient guide, is only a help, the services of which are to be used to an extent which discrimination derived from practice and experience must point out.
Many a person who thinks he is proceeding upon experience only is really making use of a mixture in which there is theory, though hie own knowledge of the process he uses, and of its history, may not be sufficient to inform him of it.
A person who uses an imperfect theory with the confidence due only to a perfect one will naturally fall into abundance of mistakes ; his predictions will be crossed by disturbing circumstances of which his theory is not able to take account, and his credit will be lowered by the failure. And inasmuch as more theories are imperfect than are perfect, and of those who attend to anything, those who acquire very sound habits of judging are few compared with those who do not get eo far, it must have happened, as it has happened, that a great quantity of mistake has been made by those who do not understand the true use of an imperfect theory. Hence much discredit has been brought upon theory in general ; and the schism of theoretical and practical men has arisen. Fortunately there are many of the former who attend properly to the improvement of imperfect theory by practice; and many calling themselves vractical.who seize with avidity all that theory can do for them, and who know that step by step theory has been making her way with giant strides into the territory of practice for the last century and a half.
By practice, as distinguished from theory, is meant (not by us, but by those who contend for the distinction) the application of that knowledge which comes from _experience only, and is not sufficiently connected with any general principles to be entitled to the name of a theory. The distinction of labourers in the field of science or art into theoretical and practical is not strictly a just one, for there ie no theorist whose knowledge is all theory, and there is no practical man whose skill is all derived from experience. But the terms will do well enough to distinguish two classes whose peculiarities it might be difficult to define exactly.
The practical man, when ho is really nothing.more, is one who can just do what he has been taught to do, and who has acquired skill and judgment in a small range of occupations. All who pride themselves upon the title would be displeased at this definition, and we readily admit that many of them are entitled to a higher character; but only because the title by which they delight to describe themselves is a wrong one. They desire, under the name of a workman, to claim the qualities of a master. The term theoretical serves, as one of contempt, to designate any thing of which they disapprove ; and as there never is any fallacy which is not carried to a fool's-cap extent by the lower order of users, it would not be difficult to make a most amusing selec tion of instances of the manner In which the distinction has been worked by the large number who are at the bottom of the class, and in whose heada it runs that their own ignorance is practical and others' knowledge theoretical. Our attention was called to this class in early youth by hearing an educated person state that he was a " practical man," by way of declining a question which involved knowledge of fractions ; it was then extracted from him, to the delight of bystanders, that all above integers is theory. And from that time whenever we wish, in a delicate way, to find out how much a person knows of his subject, we manage to ascertain to what extent he considers it practi cally useful. And we have thus discovered that what happens to ourselves happens to others, namely, that all knowledge which is possessed is practically useful, and all which is not possessed is not. It is very often noticed that men are unduly given to puff and vaunt their own professions; whereby they provoke the retort of "nothing like leather," being the words the currier used when he was asked what the city walls should be made of. The sarcasm is often unjust. The exaggerator Is frequently giving a true account of the effects of knowledge : his mistake lies only in restricting those effects to the knowledge of things in his own line, the only knowledge he has ever sufficiently cultivated.