In spite of our ignorance with respect to the meanderings of Nature,
(for of the essence of being, of their properties, their elements, their
combinations, their proportions, we yet know the simple and general
laws, according to which bodies move;) we see clearly, that some of
these laws, common to all beings, never contradict themselves; although,
on some occasions, they appear to vary, we are frequently competent to
discover that the cause becoming complex, from combination with other
causes, either impedes or prevents its mode of action being such as in
its primitive state we had a right to expect. We know that active,
igneous matter, applied to gunpowder, must necessarily cause it to
explode: whenever this effect does not follow the combination of the
igneous matter with the gunpowder--whenever our senses do not give us
evidence of the fact, we are justified in concluding, either that the
powder is damp, or that it is united with some other substance that
counteracts its explosion. We know that all the actions of man have a
tendency to render him happy: whenever, therefore, we see him labouring
to injure or destroy himself, it is just to infer that he is moved by
some cause opposed to his natural tendency; that he is deceived by some
prejudice; that, for want of experience, he is blind to consequences:
that he does not see whither his actions will lead him.

If the motion excited in beings was always simple; if their actions did
not blend and combine with each other, it would be easy to know, and we
should be assured, in the first instance, of the effect a cause would
produce. I know that a stone, when descending, ought to describe a
perpendicular: I also know, that if it encounters any other body which
changes its course, it is obliged to take an oblique direction, but if
its fall be interrupted by several contrary powers, which act upon it
alternately, I am no longer competent to determine what line it will