le what has to be expressed.

Human understanding, as it works in everyday life and in ordinary science,
is actually so constituted that it cannot penetrate into superphysical
worlds. This may be proven beyond the possibility of denial. But this
proof can have no more value for a certain kind of soul-life than the
proof one would use in showing that man's natural eye cannot, with its
visual faculty, penetrate to the smallest cells of a living being, or to
the constitution of far-off celestial bodies.

Just as the assertion is true and demonstrable that the ordinary power of
seeing does not penetrate as far as the cells, so also is the other
assertion which maintains that ordinary knowledge cannot penetrate into
supersensible worlds. And yet the proof that the ordinary power of vision
has to stop short of the cells in no way excludes the investigation of
cells. Why should the proof that the ordinary power of cognition has to
stop short of supersensible worlds, decide anything against the
possibility of investigating those worlds?

One can well sense the feeling which this comparison may evoke in many
people. One can even understand that he who doubts and holds the above
comparison against this labor of thought, does not even faintly sense the
whole seriousness of that mental effort. And yet the present writer is not
only fully convinced of that seriousness, but is of opinion that that work
of thought may be numbered among the noblest achievements of humanity. To
show that the human power of vision cannot perceive the cellular structure
without the help of instruments, would surely be a useless undertaking;
but in exact thinking, to become conscious of the nature of that thought
is a necessary work of the mind. It is only natural that one who devotes
himself to such work, should not notice that reality may refute him. The
preface to this book can be no place for entering into many "refutations"
of former editions, put forth by those who are entirely devoid of
appreciation of that for which it strives, or who direct their unfounded
attacks against the personality of the author; but it must, none the less,
be emphasized that belittling of serious scientific thought in this book
can only be imputed to the author by one who wishes to shut himself off
from the _spirit_ of what is expressed in it.

Man's power of cognition may be augmented and made more powerful, just as
the eye's power of vision may be augmented. Only the me