Poetry, music, and dancing constitute in Aristotle a group by themselves, their common element being imitation by means of rhythm—rhythm which admits of being applied to words, sounds, and the movements of the body. The history of these arts bears out the views we find expressed in Greek writers upon the theory of music; it is a witness to the primitive unity of music and poetry, and to the close alliance of the two with dancing.... The intimate fusion of the three arts afterward known as the "musical" arts—or rather we should perhaps say, the alliance of music and dancing under the supremacy of poetry—was exhibited even in the person of the artist. The office of the poet as teacher of the chorus demanded a practical knowledge of all that passed under the term "dancing," including steps, gestures, attitudes, and the varied resources of rhythmical movement.... The poet, lyric or dramatic, composed the accompaniment as well as wrote the verses; and it was made a reproach against Euripides, who was the first to deviate from the established usage, that he sought the aid of Iophon, son of Sophocles, in the musical setting of his dramas. The very word "poet" in classical times often implies the twofold character of poet and musician, and in later writers is sometimes used, like our "composer," in a strictly limited reference to music.
Aristotle does full justice to the force of rhythmic form and movement in the arts of music and dancing. The instinctive love of melody and rhythm is, again, one of the two causes to which he traces the origin of poetry, but he lays little stress on this element in estimating the finished products of the poetic art. In the Rhetoric he observes that if a sentence has metre it will be poetry; but this is said in a popular way. It was doubtless the received opinion, but it is one which he twice combats in the Poetics, insisting that it is not metrical form that makes a poem....
The general question whether metre is necessary for poetical expression has been raised by many modern critics and poets, and has sometimes been answered in the negative, as by Sidney, Shelley, Wordsworth. It is, however, worth observing that from Aristotle's point of view, which was mainly one of observation, the question to be determined was rather as to the vehicle or medium of literary mimesis; and so far as the mimesis doctrine is concerned, it is undeniable that some kinds of imaginative subject-matter are better expressed in prose, some in verse, and that Aristotle, who had before him experimental examples of writings poetic in spirit, but not metrical in form, had sufficient grounds for advocating an extension of meaning for the term poietes. But as regards the Art of Poetry, his reasoning does not lead us to conclude that he would have reckoned the authors of prose dialogues or romances among poets strictly so called. As Mr. Courthope truly says, "he does not attempt to prove that metre is not a necessary accompaniment of the higher conceptions of poetry," and he, "therefore, cannot be ranged with those who support that extreme opinion." Still there would appear to be some want of firmness in the position he takes up as to the place and importance of metre. In his definition of tragedy (chap. vi. 2) "embellished language" is included among the constituent elements of tragedy; and the phrase is then explained to mean language that has the twofold charm of metre (which is a branch of rhythm) and of melody. But these elements are placed in a subordinate rank and are hardly treated as essentials. They are in this respect not unlike scenery or spectacular effect, which, though deduced by Aristotle from the definition, is not explicitly mentioned in it. The essence of the poetry is the "imitation"; the melody and the verse are the "seasoning" of the language.... Aristotle, highly as he rates the æsthetic capacity of the sense of hearing in his treatment of music, says nothing to show that he values at its proper worth the power of rhythmical sound as factor in poetry; and this is the more striking in a Greek, whose enjoyment of poetry came through the ear rather than the eye, and for whom poetry was so largely associated with music. After all, there can hardly be a greater difference between two ways of saying the same thing than that one is said in verse, the other in prose. There are some lyrics which have lived and will always live by their musical charm, and by a strange magic that lies in the setting of the words. We need not agree with a certain modern school who would empty all poetry of poetical thought and etherealize it till it melts into a strain of music; who sing to us we hardly know of what, but in such a way that the echoes of the real world, its men and women, its actual stir and conflict, are faint and hardly to be discerned. The poetry, we are told, resides not in the ideas conveyed, not in the blending of soul and sense, but in the sound itself, in the cadence of the verse. Yet, false as this view may be, it is not perhaps more false than that other which wholly ignores the effect of musical sound and looks only to the thought that is conveyed. Aristotle comes perilously near this doctrine.
(S. H. Butcher: Aristotle's Theory of Poetry and Fine Art. pp. 138-147.)
It is not riming and versing that maketh a poet, no more than a long gown maketh an advocate; who, though he pleaded in armor, should be an advocate and no soldier. But it is that feigning notable images of virtues, vices, or what else, with that delightful teaching which must be the right describing note to know a poet by; although, indeed, the senate of poets hath chosen verse as their fittest raiment, meaning, as in matter they passed all in all, so in manner to go beyond them: not speaking (table-talk fashion, or like men in a dream) words as they chanceably fell from the mouth, but poyzing each syllable of each word by just proportion according to the dignity of the subject....
It is already said (and as I think, truly said) it is not riming and versing that maketh poesy.... But yet, presuppose it were inseparable (as, indeed, it seemeth Scaliger judgeth) truly it were an inseparable commendation. For if oratio next to ratio, speech next to reason, be the greatest gift bestowed upon mortality, that cannot be praiseless, which doth most polish that blessing of speech, which considers each word, not only (as a man may say) by his forcible quality, but by his measured quantity, carrying even in themselves a harmony, without (perchance) number, measure, order, proportion, be in our time grown odious. But lay aside the just praise it hath, by being the only fit speech for music (music, I say, the most divine striker of the senses); thus much is undoubtedly true, that if reading be foolish, without remembering, memory being the only treasurer of knowledge, those words which are fittest for memory are likewise most convenient for knowledge. Now, that verse far exceedeth prose in the knitting up of the memory, the reason is manifest. The words (besides their delight, which hath a great affinity to memory), being so set, as one word cannot be lost, but the whole work fails, which accuseth itself, calleth the remembrance back to itself, and so most strongly confirmeth it. Besides, one word so as it were begetting another, as be it in rime or measured verse, by the former a man shall have a near guess to the follower.... So that, verse being in itself sweet and orderly, and being best for memory, the only handle of knowledge, it must be in jest that any man can speak against it.
(Sir Philip Sidney: An Apologie for Poetrie.)
Versification, or the art of modulating his numbers, is indispensably necessary to a poet. Every other power by which the understanding is enlightened, or the imagination enchanted, may be exercised in prose. But the poet has this peculiar superiority, that to all the powers which the perfection of every other composition can require, he adds the faculty of joining music with reason, and of acting at once upon the senses and the passions. I suppose there are few who do not feel themselves touched by poetical melody, and who will not confess that they are more or less moved by the same thoughts, as they are conveyed by different sounds, and more affected by the same words in one order than another. The perception of harmony is, indeed, conferred upon men in degrees very unequal; but there are none who do not perceive it, or to whom a regular series of proportionate sounds cannot give delight.
(Samuel Johnson: The Rambler, No. 86.)
Various causes might be pointed out why, when the style is manly, and the subject of some importance, words metrically arranged will long continue to impart such a pleasure to mankind as he who proves the extent of that pleasure will be desirous to impart. The end of poetry is to produce excitement in coexistence with an overbalance of pleasure; but, by the supposition, excitement is an unusual and irregular state of the mind; ideas and feelings do not, in that state, succeed each other in accustomed order.... Now the co-presence of something regular, something to which the mind has been accustomed in various moods and in a less excited state, cannot but have great efficacy in tempering and restraining the passion by an intertexture of ordinary feeling, and of feeling not strictly and necessarily connected with the passion. This is unquestionably true; and hence, though the opinion will at first appear paradoxical, from the tendency of metre to divest language, in a certain degree, of its reality, and thus to throw a sort of half-consciousness of unsubstantial existence over the whole composition, there can be little doubt but that more pathetic situations and sentiments—that is, those which have a greater proportion of pain connected with them—may be endured in metrical composition, especially in rime, than in prose.... This opinion may be further illustrated by appealing to the reader's own experience of the reluctance with which he comes to the reperusal of the distressful parts of Clarissa Harlowe, or the Gamester; while Shakspere's writings, in the most pathetic scenes, never act upon us as pathetic beyond the bounds of pleasure—an effect which, in a much greater degree than might at first be imagined, is to be ascribed to small, but continual and regular impulses of pleasurable surprise from the metrical arrangement.[56] On the other hand (what it must be allowed will much more frequently happen), if the poet's words should be incommensurate with the passion, and inadequate to raise the reader to a height of desirable excitement, then (unless the poet's choice of his metre has been grossly injudicious), in the feelings of pleasure which the reader has been accustomed to connect with metre in general, and in the feeling, whether cheerful or melancholy, which he has been accustomed to connect with that particular movement of metre, there will be found something which will greatly contribute to impart passion to the words, and to effect the complex end which the poet proposes to himself.