order to ascertain to what given intuitions objects, external me,
really correspond, in other words, what intuitions belong to the
external sense and not to imagination, I must have recourse, in
every particular case, to those rules according to which experience
in general (even internal experience) is distinguished from
imagination, and which are always based on the proposition that
there really is an external experience. We may add the remark that
the representation of something permanent in existence, is not the
same thing as the permanent representation; for a representation may
be very variable and changing--as all our representations, even that
of matter, are--and yet refer to something permanent, which must,
therefore, be distinct from all my representations and external to
me, the existence of which is necessarily included in the determination
of my own existence, and with it constitutes one experience--an
experience which would not even be possible internally, if it were
not also at the same time, in part, external. To the question How?
we are no more able to reply, than we are, in general, to think the
stationary in time, the coexistence of which with the variable,
produces the conception of change.]

In attempting to render the exposition of my views as intelligible
as possible, I have been compelled to leave out or abridge various
passages which were not essential to the completeness of the work,
but which many readers might consider useful in other respects, and
might be unwilling to miss. This trifling loss, which could not be
avoided without swelling the book beyond due limits, may be
supplied, at the pleasure of the reader, by a comparison with the
first edition, and will, I hope, be more than compensated for by the
greater clearness of the exposition as it now stands.