This is from the wikipedia page:
Epistemology
Main article: Epistemology
According to the Stoics, knowledge can be attained through the application of reason to the impressions (phantasiai) received by the mind through the senses. The mind can judge (συγκατάθεσις, synkatathesis)—approve or reject—an impression, enabling it to distinguish a true representation of reality from one that is false. Some impressions can be assented to immediately, but others can achieve only varying degrees of hesitant approval, which can be labeled belief or opinion (doxa). It is only through reason that people gain clear comprehension and conviction (katalepsis). Certainty and true knowledge (episteme), achievable by the Stoic sage, can be attained only by verifying the conviction with the expertise of one's peers and the collective judgment of humankind.
Does this imply a conscious thought process to choose to accept the truth of a sense input; which animals do not have?
So i think the answer is yes - and it's more than just implication. This is the voluntary step in which a person evaluates whether to accept an impression or not.
I don't know that every statement made in that Wikipedia section is correct (especially, Certainty and true knowledge (episteme), achievable by the Stoic sage, can be attained only by verifying the conviction with the expertise of one's peers and the collective judgment of humankind. ) but that definitely seems to be the way they are going.
The section we're in right now is not by any means over so we hopefully will get a better understanding as we read further in what Cicero has to say, but I think the general outlines are becoming clear, including --
- to the Stoics certainty is possible but it is exceedingly hard to get, as true sages are "as rare as a phoenix"
- on the other hand there appear to be some impressions that they believed to be so strong that they could not possibly be false.
The Stoics are trapped in the dilemma that they refuse to accept Epicurus's view that all sensations are true, so they have to come up with some process that allows them to determine that some are true and some are false. Epicurus will revise his opinions at any point that they are contradicted by sufficient evidence from the sensations, anticipations, and feelings. The Stoics - believing in intelligent design - have to come up with something that they think is unchangeably true. ("It is only through reason that people gain clear comprehension and conviction" -- this implies reason alone is the arbiter, since the senses cannot be trusted to be honest )
And i think that problem - looking for unchangeability - is directly related to our parallel discussions about whether pleasure is a process of change and therefore inferior to a "state" that allegedly has an absolute aspect that never changes.
We've been debating whether to skip some of this in Academic Questions but currently we are seeing the sweep of arguments that Cicero is going to bring to the table about all sorts of topics that we'd better stay with it.