No accidental violation of nature's principles should be represented.

It will be necessary next for us to determine how far frequency or rarity can affect the importance of truths, and whether the artist is to be considered the most truthful who paints what is common or what is unusual in nature.

Now the whole determination of this question depends upon whether the unusual fact be a violation of nature's general principles, or the application of some of those principles in a peculiar and striking way. Nature sometimes, though very rarely, violates her own principles; it is her principle to make everything beautiful, but now and then for an instant, she permits what, compared with the rest of her works, might be called ugly: it is true that even these rare blemishes are permitted, as I have above said, for a good purpose (Part I. Sec. I. Chap. VI.); they are valuable in nature, and used as she uses them, are equally valuable (as instantaneous discords) in art; but the artist who should seek after these exclusively, and paint nothing else, though he might be able to point to something in nature as the original of every one of his uglinesses, would yet be, in the strict sense of the word, false,—false to nature, and disobedient to her laws. For instance, it is the practice of nature to give character to the outlines of her clouds by perpetual angles and right lines.