misunderstandings are possible to those who express their thoughts in
it.

Few men know exactly how much is implied in what they are saying. If I
say: All men are mortal, and an angel is not a man; therefore, an angel
is not mortal; it is not at once apparent to every one in what respect
my argument is defective. He who argues: Feathers are light; light is
contrary to darkness; hence, feathers are contrary to darkness; is
convicted of error without difficulty. But arguments of the same kind,
and quite as bad, are to be found in learned works on matters less
familiar to us, and we often fail to detect the fallacy.

Thus, Herbert Spencer argues, in effect, in the fourth and fifth
chapters of his "First Principles," as follows:--

We are conscious of the Unknowable,
The Unknowable lies behind the veil of phenomena,
Hence, we are conscious of what lies behind the veil of phenomena.

It is only the critical reader who notices that the Unknowable in the
first line is the "raw material of consciousness," and the Unknowable
in the second is something not in consciousness at all. The two senses
of the word "light" are not more different from one another. Such
apparent arguments abound, and it often requires much acuteness to be
able to detect their fallacious character.

When we take into consideration the two points indicated above, we see
that the logician is at every turn forced to reflect upon our knowledge
as men do not ordinarily reflect. He is led to ask: What is truth? He
cannot accept uncritically the assumptions which men make; and he must