"It is then a question of analyzing the circumstances and of weighing the
causes whose manifestation could determine a disparity in the results.

"We shall interest ourselves first in the surroundings for thus, as we
have said, habits of thought and feeling vary according to the epoch and
the environment.

"A comparison will be established between persons or things, in order to
be absolutely convinced of their degree of conformity.

"The state of mind in which we were when the previous events were
manifested will be considered, and we shall not fail to ascertain
plainly the similarity or change of humor at the moment as related to
that of the past.

"It is also of importance to observe the state of health, for under the
affliction of sickness things assume very easily a hostile aspect.

"It would be wrong to attribute to events judged during an illness the
same value which is given to them at this present moment.

"When one is absolutely decided as to the relation of new perceptions and
mental representations, one can calculate exactly the degree of
comparison.

"The moment will then have arrived to synthesize all the observations and
to draw from them the following deductions:

"First, like causes ought, all things being equal, to produce like
effects.