index must possess not merely the nice observation of the scholar and
the archaeologist, but also a fine sensibility. For it is the aesthetic
significance of a work that gives a clue to the state of mind that
produced it; so the ability to assign a particular work to a particular
period avails nothing unaccompanied by the power of appreciating its
aesthetic significance.

To understand completely the history of an age must we know and
understand the history of its art? It seems so. And yet the idea is
intolerable to scientific historians. What becomes of the great
scientific principle of water-tight compartments? Again, it is unjust:
for assuredly, to understand art we need know nothing whatever about
history. It may be that from works of art we can draw inferences as to
the sort of people who made them: but the longest and most intimate
conversations with an artist will not tell us whether his pictures are
good or bad. We must see them: then we shall know. I may be partial or
dishonest about the work of my friend, but its aesthetic significance is
not more obvious to me than that of a work that was finished five
thousand years ago. To appreciate fully a work of art we require nothing
but sensibility. To those that can hear Art speaks for itself: facts and
dates do not; to make bricks of such stuff one must glean the uplands
and hollows for tags of auxiliary information and suggestion; and the
history of art is no exception to the rule. To appreciate a man's art I
need know nothing whatever about the artist; I can say whether this
picture is better than that without the help of history; but if I am
trying to account for the deterioration of his art, I shall be helped by
knowing that he has been seriously ill or that he has married a wife who
insists on his boiling her pot. To mark the deterioration was to make a
pure, aesthetic judgment: to account for it was to become an historian.
To understand the history of art we must know something of other kinds