the times and what is not?

That it is natural that there should be such fluctuations of opinion,
we may freely admit. Many things influence a man to embrace a given
type of doctrine, and, as we have seen, verification is a difficult
problem. But have we here, any more than in other fields, the right to
assume that a doctrine was true at a given time merely because it
_seemed_ to men true at that time, or because they found it pleasing?
The history of science reveals that many things have long been believed
to be true, and, indeed, to be bound up with what were regarded as the
highest interests of man, and that these same things have later been
discovered to be false--not false merely for a later age, but false for
all time; as false when they were believed in as when they were
exploded and known to be exploded. No man of sense believes that the
Ptolemaic system was true for a while, and that then the Copernican
became true. We say that the former only _seemed_ true, and that the
enthusiasm of its adherents was a mistaken enthusiasm.

It is well to remember that philosophies are brought forward because it
is believed or hoped that they are true. A fairy tale may be recited
and may be approved, although no one dreams of attaching faith to the
events narrated in it. But a philosophy attempts to give us some
account of the nature of the world in which we live. If the
philosopher frankly abandons the attempt to tell us what is true, and
with a Celtic generosity addresses himself to the task of saying what
will be agreeable to us, he loses his right to the title. It is not
enough that he stirs our emotions, and works up his unrealities into
something resembling a poem. It is not primarily his task to please,
as it is not the task of the serious worker in science to please those
whom he is called upon to instruct. Truth is truth, whether it be
scientific truth or philosophical truth. And error, no matter how
agreeable or how nicely adjusted to the temper of the times, is always
error. If it is error in a field in which the detection and exposure
of error is difficult, it is the more dangerous, and the more should we
be on our guard against it.

We may, then, accept the lesson of the history of philosophy, to wit,
that we have no right to regard any given doctrine as final in such a
sense that it need no longer be held tentatively and as subject to
possible revision; but we need not, on that account, deny that
p