"The story of the beautiful," said Whistler, with the swagger that made all but his contemporaries love him, "is already complete—hewn in the marbles… - James McNeill Whistler

You shouldn't say it is not good. You should say you do not like it; and then, you know, you're perfectly safe.

[another part / version of Whistler's lecture:]
Nature contains the elements, in colour and form, of all pictures, as the keyboard contains the notes of all music. But the artist is born to pick, and choose, and group with science, these elements, that the result may be beautiful—as the musician gathers his notes, and forms his chords, until he bring forth from chaos glorious harmony. To say to the painter, that Nature is to be taken as she is, is to say to the player, that he may sit on the piano. That Nature is always right, is an assertion, artistically, as untrue, as it is one whose truth is universally taken for granted. Nature is very rarely right, to such an extent even, that it might almost be said that Nature is usually wrong: that is to say, the condition of things that shall bring about the perfection of harmony worthy a picture is rare, and not common at all.

As music is the poetry of sound, so is painting the poetry of sight, and the subject-matter has nothing to do with harmony of sound or of colour. The great musicians knew this. Beethoven and the rest wrote music — simply music; symphony in this key, concerto or sonata in that.. .Art should be independent of all claptrap — should stand alone, and appeal to the artistic sense of eye or ear, without confounding this with emotions entirely foreign to it, as devotion, pity, love, patriotism, and the like. All these have no kind of concern with it; and that is why I insist on calling my works 'arrangements' and 'harmonies.'