There are two quite different kinds of difficulty in putting the right interpretation on a statement, and a dictionary can only remove one of these, and by far the less important one. When you meet with a statement containing an unfamiliar word—say, the word "parallax," or "phanerogamous," or "brigantine"—and when you understand all the rest of the statement except that word, then as a general rule the dictionary will help to make the meaning clear. But when the difficulty is caused, not by a word being unfamiliar, but by its being used in a certain context, then the best dictionary in the world is, for your purpose, of no use at all. The nature of every dictionary is necessarily such that it entirely leaves out of account all doubts about meaning which are of this second kind. The most that a dictionary can do is to tell us the meaning of a word in those cases where the context in which it is used is not such as to make the meaning doubtful.[8][!--Note--]
In practice the words which most often need definition are those which are, as it were, shorthand symbols for perhaps a very extensive meaning. Unless the limits of this extended meaning are clearly marked out you cannot tell whether the minds of your readers are, as the lawyers say, running on all fours with your own or not. This extended meaning may be of various sorts: for example, it may be a large general principle, as in the case of "evolution" or "culture"; or it may be a general system or practice, as in the case of "commission government," "honor system," or "high standards for graduation"; or it may be a general class of things, persons, or events, as in the case of "secondary school," "professional coach," or "murder." When you use any such term in an argument, it is essential that your readers shall have the same set of details, ramifications, or instances in mind as you have yourself. For this purpose you must define the term; or, in other words, you must lay out or display the ramifications and limitations of the principle, the details of the system or practice, or the exact kinds of things, persons, or events, which you have in mind when you use the term. A few examples will make this practical meaning of defining clear.
Sometimes the definition proceeds by careful and specific limitation of the general signification of a word, as in the following example from Bagchot:
I should say that except where it is explained to the contrary, I use the word "toleration" to mean toleration by law. Toleration by society of matters not subject to legal penalty is a kindred subject, on which if I have room I will add a few words; but in the main I propose to deal with the simpler subject, toleration by law. And by toleration, too, I mean, when it is not otherwise said, toleration in the public expression of opinions; toleration of acts and practices is another allied subject, on which I can, in a paper like this, but barely hope to indicate what seems to me to be the truth, and I should add that I deal only with the discussion of impersonal doctrines: the law of libel, which deals with accusations of living persons, is a topic requiring consideration by itself.[9][!--Note--]
Sometimes the definition is rather an unfolding and displaying of the implications (from the Latin, implicare, to fold in) of the term. Huxley, near the beginning of his three "Lectures on Evolution," made sure by the following definition that his hearers should have a precise idea of what he meant by the term "evolution":
The third hypothesis, or the hypothesis of evolution, supposes that, at any comparatively late period of past time, our imaginary spectator would meet with a state of things very similar to that which now obtains; but that the likeness of the past to the present would gradually become less and less, in proportion to the remoteness of his period of observation from the present day; that the existing distribution of mountains and plains, of rivers and seas, would show itself to be the product of a slow process of natural change operating upon more and more widely different antecedent conditions of the mineral framework of the earth; until, at length, in place of that framework, he would behold only a vast nebulous mass, representing the constituents of the sun and of the planetary bodies. Preceding the forms of life which now exist our observer would see animals and plants not identical with them, but like them; increasing their differences with their antiquity and, at the same time, becoming simpler and simpler; until, finally, the world of life would present nothing but that undifferentiated protoplasmic matter, which, so far as our present knowledge goes, is the common foundation of all vital activity.
The hypothesis of evolution supposes that in all this vast progression there would be no breach of continuity, no point at which we could say, "This is a natural process," and "This is not a natural process," but that the whole might be compared to that wonderful process of development which may be seen going on every day under our eyes, in virtue of which there arises, out of the semifluid, comparatively homogeneous substance which we call an egg, the complicated organization of one of the higher animals. That, in a few words, is what is meant by the hypothesis of evolution.[10][!--Note--]
Here Huxley has laid out, in compact form the principal ramifications of the great principle of evolution, giving his hearers something like an outline map of it with its limits and principal divisions.
Where you have a practice or system to define, you will be more likely to do it by specifying the chief and essential details of the system, as in the following definition of commission government for cities. It will be noticed that this narrows down the meaning of the term to something like the Des Moines system, as distinguished from the Galveston plan.
A straight commission form of municipal government, in the judgment of Dr. Charles W. Eliot, one of its most active advocates, requires a commission composed of five members elected at large, one of whom is called the mayor, acting as chairman of the commission, but with no veto power, or any other special power not shared by the other members of the commission. The commission so elected is the source of all authority in the city, makes all ordinances, appoints all officials, collects taxes, and makes all appropriations. As set forth by its advocates, the significant features of the plan, in addition to those already mentioned, are: