Since Homer, no poet has come near Shakespeare in originality, freshness, opulence, and boldness of imagery.  It is this that forms, in a large part, the surpassing beauty of his poetry; it is in this that much of his finest idealizing centres.  And he abounds in all the figures of speech known in formal rhetoric, except the Allegory and the Apologue.  The Allegory, I take it, is hardly admissible in dramatic writing; nor is the Apologue very well suited to the place:  the former, I believe, Shakespeare never uses; and his most conspicuous instance of the latter, in fact the only one that occurs to me, is that of the Belly and the Members, so quaintly delivered to the insurgent people by the juicy old Menenius in the first scene of Coriolanus.  But, though Shakespeare largely uses all the other figures of speech, I shall draw most of what I have to say of his style in this respect, under the two heads of Simile and Metaphor, since all that can properly be called imagery is resolvable into these.  Shakespeare uses both a great deal, but the Simile in a way somewhat peculiar:  in fact, as it is commonly used by other poets, he does not seem to have been very fond of it; and when he admits it, he generally uses it in the most informal way possible.  But, first, at the risk of seeming pedantic, I will try to make some analysis of the two figures in question.

Every student knows that the Simile may be regarded as an expanded Metaphor, or the Metaphor as a condensed Simile.  Which implies that the Metaphor admits of greater brevity.  What, then, is the difference?

Now a simile, as the name imports, is a comparison of two or more things, more or less unlike in themselves, for the purpose of illustration.  The thing illustrated and the thing that illustrates are, so to speak, laid alongside each other, that the less known may be made more intelligible by the light of that which is known better.  Here the two parts are kept quite distinct, and a sort of parallel run between them.  And the actions or the qualities of the two things stand apart, each on their own side of the parallel, those of neither being ascribed to the other.  In a metaphor, on the other hand, the two parts, instead of lying side by side, are drawn together and incorporated into one.  The idea and the image, the thought and the illustration, are not kept distinct, but the idea is incarnated in the image, so that the image bears the same relation to the idea as the body does to the soul.  In other words, the two parts are completely identified, their qualities interfused and interpenetrating, so that they become one.  Thus a metaphor proceeds by ascribing to a given object certain actions or qualities which are not literally true of that object, and which have in reference to it only the truth of analogy.