principle of beauty in all things. Keats was always very sensitive to
the mysterious effects of moonlight, and so for him the moon became a
symbol for the great abstract principle of beauty, which, during the
whole of his poetic life, he worshipped intellectually and spiritually.
"The mighty abstract Idea I have of Beauty in all things stifles the
more divided and minute domestic happiness," he writes to his brother
George; and the last two well-known lines of the _Ode on a Grecian Urn_
fairly sum up his philosophy--

Beauty is truth, truth Beauty, that is all
Ye know on earth, and all ye need to know.

So that the moon represents to Keats the eternal idea, the one essence
in all. This is how he writes of it, in what is an entirely mystical
passage in _Endymion_--

... As I grew in years, still didst thou blend
With all my ardours: thou wast the deep glen;
Thou wast the mountain-top, the sage's pen,
The poet's harp, the voice of friends, the sun;
Thou wast the river, thou wast glory won;
Thou wast my clarion's blast, thou wast my steed,
My goblet full of wine, my topmost deed:
Thou wast the charm of women, lovely Moon!

In his fragment of _Hyperion_, Keats shadows forth the unity of all
existence, and gives magnificent utterance to the belief that change is
not decay, but the law of growth and progress. Oceanus, in his speech to
the overthrown Titans, sums up the whole meaning as far as it has gone,
in verse which is unsurpassed in English--