In contradiction to Plato's view that the Ideas, or Prototypes,
of phenomena alone really exist, the Stoics held that material objects
alone existed; but immanent in the material universe was a spiritual
force which acted through them, manifesting itself under many forms,
as fire, aether, spirit, soul, reason, the ruling principle.

The universe, then, is God, of whom the popular gods
are manifestations; while legends and myths are allegorical.
The soul of man is thus an emanation from the godhead,
into whom it will eventually be re-absorbed. The divine ruling
principle makes all things work together for good, but for
the good of the whole. The highest good of man is consciously
to work with God for the common good, and this is the sense
in which the Stoic tried to live in accord with nature.
In the individual it is virtue alone which enables him to do this;
as Providence rules the universe, so virtue in the soul
must rule man.

In Logic, the Stoic system is noteworthy for their theory
as to the test of truth, the Criterion. They compared
the new-born soul to a sheet of paper ready for writing.
Upon this the senses write their impressions, fantasias and
by experience of a number of these the soul unconsciously
conceives general notions koinai eunoiai or anticipations.
prolhyeis When the impression was such as to be irresistible
it was called (katalnptikh fantasia) one that holds fast,
or as they explained it, one proceeding from truth.
Ideas and inferences artificially produced by deduction
or the like were tested by this 'holding perception.'
Of the Ethical application I have already spoken.