distinguished from that which had not? "By the feel" is all that the
Stoics really had to say in answer to this question. Just as Hume
made the difference between sense-impressions and ideas to lie in the
greater vividness of the former, so did they; only Hume saw no
necessity to go beyond the impression, whereas the Stoics did.
Certain impressions, they maintained, carried with them an
irresistible conviction of their own reality, and this, not merely in
the sense that they existed; but also that they were referable to an
external cause. These were called "gripping phantasies." Such a
phantasy did not need proof of its own existence, or of that of its
object. It possessed self-evidence. Its occurrence was attended with
yielding and assent on the part of the soul. For it is as natural for
the soul to assent to the self-evident as it is for it to pursue its
proper good. The assent to a griping phantasy was called
"comprehension," as indicating the firm hold that the soul thus took
of reality. A gripping phantasy was defined as one which was stamped
and impressed from an existing object, in virtue of that object
itself, in such a way as it could not be from a non-existent object.
The clause "in virtue of that object itself" was put into the
definition to provide against such a case as that of the mad Orestes,
who takes his sister to be a Fury. There the impression was derived
from an existing object, but not from that object as such, but as
coloured by the imagination of the percipient.

The criterion of truth then was no other than the gripping phantasy.
Such at least was the doctrine of the earlier Stoics, but the later
added a saving clause, "when there is no impediment." For they were
pressed by their opponents with such imaginary cases as that of
Admetus, seeing his wife before him in very deed, and yet not
believing it to be her. But here there was an impediment. Admetus did