"Looking back we can see how indirectly we know the environment in which
nevertheless we live... whatever we believe to be a true picture, we treat as if
it were the environment itself.
It is harder to remember that about
the beliefs upon which we are now acting, but in respect to other peoples and
other ages we flatter ourselves that it is easy to see when they were in deadly
earnest about ludicrous pictures of the world. We insist, because of our
superior hindsight, that the world as they needed to know it, and the world as
they did know it, were often two quite contradictory things."