"It is clear, in fact, from an invincible necessity, that the
human mind can observe directly all phenomena except its own.
For by whom can the observation be made? It is conceivable
that, relatively to moral phenomena, man can observe himself in
regard to the passions which animate him, from this anatomical
reason, that the organs which are the seat of them are distinct
from those destined to the function of observation. Though each
man has had occasion to make on himself such observations, yet
they can never have any great scientific importance; and the
best means of knowing the passions will be always to observe
them without; [_indeed_!] for every state of passion very
energetic--that is to say, precisely those which it would be
most essential to examine, are necessarily incompatible with
the state of observation. But as to observing in the same
manner intellectual phenomena, while they are proceeding, it is
manifestly impossible. The thinking individual cannot separate
himself in two parts, of which the one shall reason, and the
other observe it reasoning. The organ observed and the organ
observing being in this case identical, how can observation be
carried on?

"This pretended psychological method is thus radically absurd.
And only consider to what procedures profoundly contradictory
it immediately conducts! On the other hand, they recommend you
to isolate yourself as much as possible from all external
sensation; and, above all, they interdict you every
intellectual exercise; for if you were merely occupied in
making the most simple calculation, what would become of your
_internal_ observation? On the other hand, after having thus,