d, without any danger of obscurity or mistake.

In this research we meet with very little encouragement from that
prodigious diversity, which is found in the opinions of those
philosophers, who have pretended to explain the secret force and energy
of causes. [See Father Malbranche, Book vi. Part 2, chap. 3. And the
illustrations upon it.] There are some, who maintain, that bodies
operate by their substantial form; others, by their accidents or
qualities; several, by their matter and form; some, by their form and
accidents; others, by certain virtues and faculties distinct from all
this. All these sentiments again are mixed and varyed in a thousand
different ways; and form a strong presumption, that none of them have
any solidity or evidence, and that the supposition of an efficacy in any
of the known qualities of matter is entirely without foundation.
This presumption must encrease upon us, when we consider, that these
principles of substantial forms, and accidents, and faculties, are not
in reality any of the known properties of bodies, but are perfectly
unintelligible and inexplicable. For it is evident philosophers would
never have had recourse to such obscure and uncertain principles, had
they met with any satisfaction in such as are clear and intelligible;
especially in such an affair as this, which must be an object of the
simplest understanding, if not of the senses. Upon the whole, we
may conclude, that it is impossible in any one instance to shew the
principle, in which the force and agency of a cause is placed; and that
the most refined and most vulgar understandings are equally at a loss
in this particular. If any one think proper to refute this assertion,
he need not put himself to the trouble of inventing any long reasonings:
but may at once shew us an instance of a cause, where we discover the
power or operating principle. This defiance we are obliged frequently
to make use of, as being almost the only means of proving a negative in
philosophy.

The small success, which has been met with in all the attempts to fix
this power, has at last obliged philosophers to conclude, that the
ultimate force and efficacy of nature is perfectly unknown to us,
and that it is in vain we search for it in all the known qualities of
matter. In this opinion they are almost unanimous; and it is only in the
inference they draw from it, that they discover any difference in their
sentiments. For some of them, as the CARTESIANS in