The question is then not really whether poetry should be concerned with moral, sociological or psychological themes, for these themes always have poetry in them, and an emotional treatment of them brings the poetry into prominence. Ideas are the substance of poetry and nearly all ideas are moral, sociological or psychological. Even scientific facts and metaphysical utterances may be so stated by a writer as to show the latent poetry. The two famous passages in _Leaves of Grass_ beginning "I open my scuttle at night" and "I am an acme of things accomplished and an encloser of things to be" are emotional statements of the facts of the infinity of the universe and of the evolution of man, respectively; Whitman brought out the poetry in a philosophical and in a scientific idea.
Moral views may be imaginatively treated and be poetry. The theme of _Great Expectations_ is a sermon against pride and snobbery, and the emotional treatment, especially by force of example, makes part of the book poetry. Portrayals of hypocrites, for instance, so truthfully and movingly artistic as to arouse an ecstatic state in the reader, become poetry. Hence Tartuffe and Pecksniff are poetical portraits, even when drawn in prose.
Poetry was supposed to appeal to the imagination, prose to the intellect; poetry was presumed to be dictated by the heart, prose by the mind; fancy was thought to hold sway in poetry, logic in prose. But nevertheless, the great English poets like Shakespeare, Browning, Shelley, Wordsworth, Whitman, gave us much poetry that was produced by the intellect, weighed by the mind, and governed by logic. Any intellectual and even moral performance may be elevated into poetry, when emotionally and ecstatically presented. And philosophers like Plato, Pascal, Schopenhauer and Nietzsche have demonstrated this.
Our definition of poetry throws much light on the subject of the relations of politics and morals, of social and philosophical problems to poetry. Poets should instruct, while delighting, is the contention of one group. They ought merely to express beauty and emotions, is the emphatic demand of another class. I doubt if there has ever been a great poet who hasn't done both of these things. If a poet is to teach he must teach something; he must express ideas, and ideas mean thoughts about life, and these in turn refer to the relations of man to himself, to one another, to the opposite sex, to society, to the universe, to nature. But it is while doing this that he must give us beauty and emotion.