One should no more look for a chapter on the drama in a book like this dealing with poetry than for a treatise on the novel. A drama, considered merely as a series of scenes bound together by a plot in a fit manner to be presented on the stage to move people, and based on rules that relate to economy of words, concentration of facts and strikingness of action, is a performance that has a technique of its own; the dramatist is a poet only by virtue of the ecstasy he puts in the work. Considered in its primary significance as a performance where action is the chief feature, the drama becomes poetry in those parts where the action and emotion are concentrated.
It is, however, often difficult to extract scenes from the play, as they lose in effectiveness by being thus separated. But the fact remains that there is no such thing as dramatic poetry, for the essence of all poetry is its lyricism. Dramatic scenes contain the lyric cries of the _dramatis personæ_. Action is but the emotional disturbances of the characters and no longer merely means violent conduct, surprises, battles, duels, suicides, murders. All great novels have dramatic scenes and they are often as exuberant in poetry as are similar scenes in plays. We no longer regard as tragedies only those plays in verse where a virtuous person of high degree is in a frightful predicament because of unjust and unlooked-for defeat with fate. No, in spite of Aristotle, the suffering of even a wicked person of low station, depicted as due to his own fault as of Hurstwood in _Sister Carrie_, and described in prose narrative, is also tragedy. There is incidentally no such thing as a comic dramatic poem, but a comic scene may be poetic if it moves to ecstasy (not merely to farcic laughter), and if it is essentially lyrical. Comedy also appears in works of fiction in prose, and may be poetical. Moreover, most performances in prose dialogue or fiction present an admixture of tragic and comic.
Tragedy often presents lyric poems greater than any other work of literature; hence Aristotle and his imitators concluded that a verse tragedy was the highest form of poetry. This is not so. If Shakespeare and Sophocles lived in our day they might have written novels or essays, and I daresay with their genius those novels or essays would have been as good as their plays and would have contained as great poetry.