In the second case, on the contrary, the act of refraining from assenting will be the result of a practical decision, an act which, far from being natural and spontaneous, will probably demand a great deal of effort and training (15).
Unlike the vicious individual, Epictetus moral progressor does not assent to impressions as soon as they come to his mind, but rather stops to examine them (diakrino, dokimazo) (26) before assenting to or rejecting them.
Ifwe interpret those passages in this way, we are making room for the possibility that we may voluntarily refrain from assenting to a certain impression, and yet not be able to act contrary to it as long as we have not ruled it out as false.
Whether or not we critically examine our impressions before assenting to or rejecting them, that act is not the operation of a neutral, transcendental faculty which might be considered to be independent from our epistemic history.
If we go back to Epictetus' demand for a critical examination of our impression and to the idea that ought implies can, a serious problem seems to arise, which is that, if our acts of assent are an expression of our epistemic disposition, DC seems to make no sense from a practical point of view, because whether or not I critically examine my impressions before assenting to them depends on my epistemic disposition.
on the ideas or principles (69) that are being exercised: it is not the act of repeating to ourselves any piece of knowledge that contributes to our moral progress; moreover, the goal of critically assenting only to true impressions can be reached only if the correct beliefs are at hand whenever we are faced with any given impression.
Even if we grant that a critical analysis of the impressions that come to my mind is a necessary condition for my actions (or at least my impulses (70)) to be virtuous, it is certainly not a sufficient condition--after all, I can spend days or even months deliberating about whether the impression 'it is kathekon to do X' is true or not, and yet end up assenting to the wrong alternative.
In other words, if we did not have the capacity to voluntarily refrain from assenting even in cases where the impression appears to us to be completely truthful, Epictetus demand that we exercise or perform a critical examination of our impressions would be a demand that we could not possibly meet.
Given that the passage does not focus on the rash assent of the vicious individual, it might be taken to mean that there is no critical assessment at all of an impression before assenting to it, given that we assent euthus.