from the whole procession of systems best summed up in the dictum of
Protagoras: "Man is the measure of all things"--each has his own truth,
and this need not be truth to another?

This, I say, is a first impression and a natural one. I hasten to add:
this should not be the last impression of those who read with
thoughtful attention.

One thing should be emphasized at the outset: nothing will so often
bear rereading as the history of philosophy. When we go over the
ground after we have obtained a first acquaintance with the teachings
of the different philosophers, we begin to realize that what we have in
our hands is, in a sense, a connected whole. We see that if Plato and
Aristotle had not lived, we could not have had the philosophy which
passed current in the Middle Ages and furnished a foundation for the
teachings of the Church. We realize that without this latter we could
not have had Descartes, and without Descartes we could not have had
Locke and Berkeley and Hume. And had not these lived, we should not
have had Kant and his successors. Other philosophies we should
undoubtedly have had, for the busy mind of man must produce something.
But whatever glimpses at the truth these men have vouchsafed us have
been guaranteed by the order of development in which they have stood.
They could not independently have written the books that have come down
to us.

This should be evident from what has been said earlier in this chapter
and elsewhere in this book. Let us bear in mind that a philosopher
draws his material from two sources. First of all, he has the
experience of the mind and the world which is the common property of us
all. But it is, as we have seen, by no means easy to use this