ng done, some are
quiet some passive, some, as it were, senseless; as, place, time,
materials, tools, and other things of the same sort. But some exhibit
a sort of preparatory process towards the production of the effect
spoken of; and some of themselves do contribute some aid to it;
although it is not indispensable; as meeting may have supplied
the cause to love; love to crime. From this description of causes
depending on one another in infinite series, is derived the doctrine
of fate insisted on by the Stoics. And as I have thus divided the
genera of causes, without which nothing can be effected, so also the
genera of the efficient causes can be divided in the same manner. For
there are some causes which manifestly produce the effect, without any
assistance from any quarter; others which require external aid; as for
instance, wisdom alone by herself makes men wise; but whether she is
able alone to make men happy is a question.

XVI. Wherefore, when any cause efficient as to some particular end has
inevitably presented itself in a discussion, it is allowable without
any hesitation to conclude that what that cause must inevitably effect
is effected. But when the cause is of such a nature that it does not
inevitably effect the result, then the conclusion which follows is
not inevitable And that description of causes which has an inevitable
effect does not usually engender mistakes; but this description,
without which a thing cannot take place, does often cause perplexity.
For it does not follow, because sons cannot exist without parents,
that there was therefore any unavoidable cause in the parents to have
children. This, therefore, without which an effect cannot be produced,
must be carefully separated from that by which it is certainly
produced. For that is like--

"Would that the lofty pine on Pelion's brow
Had never fall'n beneath the woodman's axe!"

For if the beam of fir had never fallen to the ground, that Argo
would not have been built; and yet there was not in the beams any
unavoidably efficient power. But when

"The fork'd and fiery bolt of Jove"

was hurled at Ajax's vessel, that ship was then inevitably burnt.

And again, there is a difference between causes, because some are such
that without any particular eagerness of mind, without any expressed
desire or opinion, they effect what is, as it were, their own work;
as for instance, "that everything must die which has been born." But
other res