Emotions, held the Stoics, are up to us. We are and should be in control of our emotions, which are the products of mistaken judgments of our assenting to external things, which are not up to us. The assent to an external impression wouldn’t be a problem in itself if it wasn’t also accompanied by an unconscious value judgment about the external thing. When we feel an emotion, it is because we have assented to something outside of us and have decided that this thing is either good or bad. For example, I see a dog walking next to me and by assenting to the impression of the dog, I make a value judgment: “I see a big and scary dog which can bite and kill me, and this is bad!” This gives rise to fear in me, and I immediately cross the street and walk on the other sidewalk. Was this a rational judgment? Was the dog really going to bite me? That matters little for the Stoics. What matters most is that the judgment I made would make no difference to the dog, which would bite me or not bite me regardless of my feelings about it. The proper and rational way to have reacted would be to respond to the dog, as to any external impression, with complete indifference. My mental assertion should therefore have been: “I see a dog,” and simply that. I would stay internally stable, whether the dog decided to defile me or not.
Placing a “good” value on something doesn’t mean that this will elicit a positive emotion, either. All emotions that arise as the result of assenting to external things, places, or people are “illnesses of the soul”, because they are not the result of purely rational judgments.
The Stoics did in fact believe that there are good emotions–feelings that can be part of a rational mind–but these are emotions that are self-sufficient; they are emotions that deal only with internal things and are part of the (presumably) rational inner self, so they would have to belong to the completely virtuous person, which for them would be the sage.
In his book on the Stoics, John Sellars lays out a chart of how all emotions that arise out of judgments of externals, whether good or bad, are essentially always “bad.” This is partly because even if a positive emotion arises, it is bound to be temporary and fickle due to its connection to things we have no control over. And once that good emotion goes away, it gives rise to much more powerful and persistent bad emotions. All good emotions do, in the end, is rouse up our internal state and leave us worse off than before. So not making value judgments about external impressions is a wise thing to do so as to prevent the illness of the soul.
Here’s the breakdown, based on Sellars’ explanation:
If a good emotion is present, it results in delight due to the belief in a present good.
If a good emotion is absent, it gives rise to lust due to the belief in a future good.
If a bad emotion is present, it causes distress and the belief in a present evil.
If a bad emotion is absent, it leads to fear and the belief in a future evil.
All of the above, with the exception of delight, have something negative already built into them. But as mentioned, even delight is fleeting so it doesn’t amount to much in the grand scheme. The three “good emotions” for the Stoics are joy (instead of pleasure), caution (instead of fear), and wishing (instead of desire). These are emotions that depend on nothing but inner contentment, and that can be cultivated inside of us independently of anything external. They are, for that reason, rational emotions. But even having these emotions is to fall short of the true ethical ideal, apatheia, which is freedom from all emotion.