itself, objectively, but the moment he reflects on his
own knowledge he catches himself red-handed in the
act of upholding his knowledge. He finds himself as-
serting it to be true, and this asserting and believing is
an action which makes an addition to the world on
which his knowledge bears. So every time we acquire
knowledge we enlarge the world, the world of man,
by something that is not yet incorporated in the object
of the knowledge we hold, and in this sense a compre-
hensive knowledge of man must appear impossible.

The significance which I attribute to this logical
oddity will become apparent in the solution suggested
for it. Its solution seems to lie in the fact that
human knowledge is of two kinds. What is usually
described as knowledge, as set out in written words or
maps, or mathematical formulae, is only one kind of
knowledge; while unformulated knowledge, such as
we have of something we are in the act of doing, is an-
other form of knowledge. If we call the first kind ex-
plicit knowledge, and the second, tacit knowledge, we
may say that we always know tacitly that we are holding
our explicit knowledge to be true. If, therefore, we are
satisfied to hold a part of our knowledge tacitly, the
vain pursuit of reflecting ever again on our own reflec-
tions no longer arises. The question is whether we can
be satisfied with this. Tacit knowing appears to be a
doing of our own, lacking the public, objective, charac-

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