estimate that we know nothing if we only know something; it is itself that
insistence and that tendency: without that it would not exist. Let us pause
there for the moment. Man knows of nature only those impressions which he
receives from it, co-ordinated by the forms of sensibility, and further the
ideas of it which he preserves co-ordinated by the forms of his
understanding. This is very little. It is all, if we consider only pure
reason.

PRACTICAL REASON.--_But_ there is perhaps another reason, or
another aspect of reason--to wit, practical reason. What is practical
reason? Something in us tells us: you should act, and you should act in
such a way; you should act rightly; this is not right, so do not do it;
that is right, do it. As a fact this is uncontestable. What is the
explanation? From what data of experience, from what systematization of
the understanding has our mind borrowed this? Where has it got it? Does
nature yield obedience to a "you ought"? Not at all. It exists, and it
develops and it goes its way, according to our way of seeing it in time and
space, and that is all. Does the understanding furnish the idea of "you
ought"? By no means; it gives us ideas of quantity, of quality, of cause
and effect, etc., and that is all; there is no "you ought" in all
that. Therefore this "you ought" is purely human; it is the only principle
which comes exactly from ourselves only. It might therefore well be the
very foundation of us.--It may be an illusion.--No doubt, but it is highly
remarkable that it exists, though nothing gives it birth or is of a nature
to give it birth. An illusion is a weakness of the senses or an error of
logic and is thus explained; but an illusion in itself and by itself and
only proceeding from itself is most singular and not to be explained as an
illusion. Hence it remains that it is a reality, a reality of our nature,
and given the coercive force of its voice and act, it is the most real
reality there is in us.