Masks are arrested expressions and admirable echoes of feeling, at once faithful, discreet, and superlative. Living things in contact with the air must acquire a cuticle, and it is not urged against cuticles that they are not hearts; yet some philosophers seem to be angry with images for not being things, and with words for not being feelings. Words and images are like shells, no less integral parts of nature than are the substances they cover, but better addressed to the eye and more open to observation. I would not say that substance exists for the sake of appearance, or faces for the sake of masks, or the passions for the sake of poetry and virtue. Nothing arises in nature for the sake of anything else; all these phases and products are involved equally in the round of existence, and it would be sheer wilfulness to praise the germinal phase on the ground that it is vital, and to denounce the explicit phase on the ground that it is dead and sterile. We might as justly despise the seed for being merely instrumental, and glorify the full-blown flower, or the conventions of art, as the highest achievement and fruition of life. Substance is fluid, and, since it cannot exist without some form, is always ready to exchange one form for another; but sometimes it falls into a settled rhythm or recognizable vortex, which we call a nature, and which sustains an interesting form for a season. These sustained forms are enshrined in memory and worshipped in moral philosophy, which often assigns to them a power to create and to reassert themselves which their precarious status is very far from justifying. But they are all in all to the mind: art and happiness lie in pouring and repouring the molten metal of existence through some such tenable mould.