The use of similes and metaphors and other figurative language raises a difficult question.  On the whole, perhaps the best advice about using them is, Don’t unless you have to.  In other words, where a figure of speech is a necessity of expression, where you cannot make your thought clear and impart to it the warmth of feeling with which it is clothed in your own mind except by a touch of imaginative color, then use a figure of speech, if one flashes itself on your mind.  If you add it deliberately as adornment of your speech, it will strike a false note; if you laboriously invent it the effort will show.  Unless your thought and your eagerness for your subject flow naturally and inevitably into an image, it is better to stick to plain speech, for any suggestion of insincerity is fatal to the persuasiveness of an argument.

The value of the figure of speech is chiefly in giving expression to feelings which cannot be set forth in abstract words, the whole of whose meaning can be defined:  in the connotation of words—­that indefinable part of their meaning which consists in their associations, implications, and general emotional coloring—­lies their power to clothe thought with the rich color of feeling which is the life.  At the same time, they serve as a fillip to the attention.  There are not very many people who can long keep the mind fixed on a purely abstract line of thought, and none can do it without some effort.  Professor William James is a notable example of a writer whose thought flowed spontaneously into necessary figures of speech: 

When one turns to the magnificent edifice of the physical sciences, and sees how it was reared; what thousands of disinterested moral lives of men lie buried in its mere foundations; what patience and postponement, what choking down of preference, what submission to the icy laws of outer fact are wrought into its very stones and mortar; how absolutely impersonal it stands in its vast augustness,—­then how besotted and contemptible seems every little sentimentalist who comes blowing his voluntary smoke wreaths, and pretending to decide things out of his private dream.[63]

One cannot go to sleep over a style like that, for besides the obvious sincerity and rush of warm feeling, the vividness of the figures is like that of poetry.  On the either hand, one must remember that it is given to few men to attain the unstudied eloquence of Professor James.

Fables and anecdotes serve much the same purpose, but more especially throw into memorable form the principle which they are intended to set forth.  There are a good many truths which are either so complex or so subtle that they defy phrasing in compact form, yet their truth we all know by intuition.  If for such a truth you can find a compact illustration, you can leave it much more firmly fixed in your readers’ minds than by any amount of systematic exposition.  Lincoln in his Springfield speech, for example, threw into striking form the feeling which was so common in the North, that each step forward in the advance of slavery so fitted into all earlier ones that something like a concerted plan must be assumed: