Edgar Allan Poe says

I hold that a long poem does not exist. I maintain that the phrase, "a long poem," is simply a flat contradiction in terms.

I need scarcely observe that a poem deserves its title only inasmuch as it excites, by elevating the soul. The value of the poem is in the ratio of this elevating excitement. But all excitements are, through a psychal necessity, transient. That degree of excitement which would entitle a poem to be so called at all, cannot be sustained throughout a composition of any great length….

On the other hand, it is clear that a poem may be improperly brief. Undue brevity degenerates into mere epigrammatism. A very short poem, while now and then producing a brilliant or vivid, never produces a profound or enduring effect. There must be the steady pressing down of the stamp upon the wax….

While the epic mania, while the idea that to merit in poetry prolixity is indispensable, has for some years past been gradually dying out of the public mind, by mere dint of its own absurdity, we find it succeeded by a heresy too palpably false to be long tolerated, but one which, in the brief period it has already endured, may be said to have accomplished more in the corruption of our Poetical Literature than all its other enemies combined. I allude to the heresies of The Didactic. It has been assumed, tacitly and avowedly, directly and indirectly, that the ultimate object of all Poetry is Truth. Every poem, it is said, should inculcate a moral, and by this moral is the poetical merit of the work to be adjudged…. We have taken it into our heads that to write a poem simply for the poem's sake, and to acknowledge such to have been our design, would be to confess ourselves radically wanting in the true poetic dignity and force: -- but the simple fact is that would we but permit ourselves to look into our own souls we should immediately there discover that under the sun there neither exists nor can exist any work more thoroughly dignified, more supremely noble, than this very poem, this poem per se, this poem which is a poem and nothing more, this poem written solely for the poem's sake.

With as deep a reverence for the True as ever inspired the bosom of man, I would nevertheless limit, in some measure, its modes of inculcation. I would limit to enforce them. I would not enfeeble them by dissipation. The demands of Truth are severe. She has no sympathy with the myrtles. All that which is so indispensable in Song is precisely all that with which she has nothing whatever to do. It is but making her a flaunting paradox to wreathe her in gems and flowers. In enforcing a truth we need severity rather than efflorescence of language. We must be simple, precise, terse. We must be cool, calm, unimpassioned. In a word, we must be in that mood which, as nearly as possible, is the exact converse of the poetical. He must be blind indeed who does not perceive the radical and chasmal difference between the truthful and the poetical modes of inculcation. He must be theory-mad beyond redemption who, in spite of these differences, shall still persist in attempting to reconcile the obstinate oils and waters of Poetry and Truth.

Dividing the world of mind into its three most immediately obvious distinctions, we have the Pure Intellect, Taste, and the Moral Sense…. Just as the Intellect concerns itself with Truth, so Taste informs us of the Beautiful, while the Moral Sense is regardful of Duty. Of this latter, while Conscience teaches the obligation, and Reason the expediency, Taste contents herself with displaying the charms: -- waging war upon Vice solely on the ground of her deformit -- her disproportion -- her animosity to the fitting, to the appropriate, to the harmonious -- in a word, to Beauty.

An immortal instinct deep within the spirit of man is thus plainly a sense of the Beautiful. This it is which administers to his delight in the manifold forms, and sounds, and odors and sentiments amid which he exists. And just as the lily is repeated in the lake, or the eyes of Amaryllis in the mirror, so is the mere oral or written repetition of these forms, and sounds, and colors, and odors, and sentiments a duplicate source of delight. But this mere repetition is not poetry. He who shall simply sing, with however glowing enthusiasm, or with however vivid a truth of description, of the sights, and sounds, and odors, and colors, and sentiments which greet him in common with all mankind -- he, I say, has yet faded to prove his divine title. There is still a something in the distance which he has been unable to attain. We have still a thirst unquenchable, to allay which he has not shown us the crystal springs. This thirst belongs to the immortality of Man. It is at once a consequence and an indication of his perennial existence. It is the desire of the moth for the star. It is no mere appreciation of the Beauty before us, but a wild effort to reach the Beauty above. Inspired by an ecstatic prescience of the glories beyond the grave, we struggle by multiform combinations among the things and thoughts of Time to attain a portion of that Loveliness whose very elements perhaps appertain to eternity alone. And thus when by Poetry, or when by Music, the most entrancing of the poetic moods, we find ourselves melted into tears, we weep then, not  … through excess of pleasure, but through a certain petulant, impatient sorrow at our inability to grasp now, wholly, here on earth, at once and for ever, those divine and rapturous joys of which through the poem, or through the music, we attain to but brief and indeterminate glimpses….

To recapitulate then: -- I would define, in brief, the Poetry of words as The Rhythmical Creation of Beauty. Its sole arbiter is Taste. With the Intellect or with the Conscience it has only collateral relations. Unless incidentally, it has no concern whatever either with Duty or with Truth.

A few words, however, in explanation. That pleasure which is at once the most pure, the most elevating, and the most intense, is derived, I maintain, from the contemplation of the Beautiful. In the contemplation of Beauty we alone find it possible to attain that pleasurable elevation, or excitement of the soul, whichwe recognise as the Poetic Sentiment, and which is so easily distinguished from Truth, which is the satisfaction of the Reason, or from Passion, which is the excitement of the heart. I make Beauty, therefore -- using the word as inclusive of the sublime -- I make Beauty the province of the poem, simply because it is an obvious rule of Art that effects should be made to spring as directly as possible from their causes: -- no one as yet having been weak enough to deny that the peculiar elevation in question is at least most readily attainable in the poem. It by no means follows, however, that the incitements of Passion, or the precepts of Duty, or even the lessons of Truth, may not be introduced into a poem, and with advantage, for they may subserve incidentally, in various ways, the general purposes of the work: but the true artist will always contrive to tone them down in proper subjection to that Beauty which is the atmosphere and the real essence of the poem.

Thus, although in a very cursory and imperfect manner, I have endeavoured to convey to you my conception of the Poetic Principle. It has been my purpose to suggest that, while this principle itself is strictly and simply the Human Aspiration for Supernal Beauty, the manifestation of the Principle is always found in an elevating excitement of the soul, quite independent of that passion which is the intoxication of the Heart, or of that truth which is the satisfaction of the Reason. For in regard to passion, alas! its tendency is to degrade rather than to elevate the Soul. Love, on the contrary -- Love -- the true, the divine Eros -- the Uranian as distinguished from the Dionnan Venus -- is unquestionably the purest and truest of all poetical themes. And in regard to Truth, if, to be sure, through the attainment of a truth we are led to perceive a harmony where none was apparent before, we experience at once the true poetical effect; but this effect is referable to the harmony alone, and not in the least degree to the truth which merely served to render the harmony manifest. 

We shall reach, however, more immediately a distinct conception of what the true Poetry is, by mere reference to a few of the simple elements which induce in the Poet himself the true poetical effect. He recognises the ambrosia which nourishes his soul in the bright orbs that shine in Heaven -- in the volutes of the flower -- in the clustering of low shrubberies -- in the waving of the grain-fields -- in the slanting of tall eastern trees -- in the blue distance of mountains -- in the grouping of clouds -- in the twinkling of half-hidden brooks -- in the gleaming of silver rivers -- in the repose of sequestered lakes -- in the star-

mirroring depths of lonely wells. He perceives it in the songs of birds -- in the harp of Aeolus -- in the sighing of the night-wind -- in the repining voice of the forest -- in the surf that complains to the shore -- in the fresh breath of the woods -- in the scent of the violet -- in the voluptuous perfume of the hyacinth -- in the suggestive odour that comes to him at eventide from far-distant undiscovered islands, over dim oceans, illimitable and unexplored. He owns it in all noble thoughts -- in all unworldly motives -- in all holy impulses -- in all chivalrous, generous, and self-sacrificing deeds. He feels it in the beauty of woman -- in the grace of her step -- in the lustre of her eye -- in the melody of her voice -- in her soft laughter, in her sigh -- in the harmony of the rustling of her robes. He deeply feels it in her winning endearments -- in her burning enthusiasms -- in her gentle charities -- in her meek and devotional endurances -- but above all -- ah, far above all he kneels to it -- he worships it in the faith, in the purity, in the strength, in the altogether divine majesty -- of her love.