On how do you tell apart a bad opinion from a good one, the ancient Stoics (lately I'm quoting them more, as I'm immersed in their writings) have some thoughts here. For the longer version, you have to read their works[1], but to give an extremely simplified version, without butchering the concept:
The Stoics have this notion of 'impression' and 'assent'. It goes like this: An impression of walking strikes you. But only after you told yourself "yes, it is fitting for me to walk", thus giving your 'assent' (agreement) to it, will you actually go for a walk. Of course, we know that we don't actually verbalize like that; as it all happens too quickly. Their goal here is to not evade responsibility to shape ones own judgements, opinions, and even emotions "in accordance with reason".
Thus, the Greek philosopher Epictetus' favourite way of describing the Stoic project is: "making correct use of mental impressions".
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The same technique of impression/assent is also used, along with others, to diagnose "passions" (Greek, páthos—it's a loaded word that is used to categorize many emotions, including the debilitating ones). Thus, for the Stoics, the cause of any "passion" is an "error of judgement". What sort of error? Mistaken system of values—there's a ton more to this, but I have to skip it for brevity's sake. FWIW, some reading recommendations on this topic on a thread here[1].
The Stoics have this notion of 'impression' and 'assent'. It goes like this: An impression of walking strikes you. But only after you told yourself "yes, it is fitting for me to walk", thus giving your 'assent' (agreement) to it, will you actually go for a walk. Of course, we know that we don't actually verbalize like that; as it all happens too quickly. Their goal here is to not evade responsibility to shape ones own judgements, opinions, and even emotions "in accordance with reason".
Thus, the Greek philosopher Epictetus' favourite way of describing the Stoic project is: "making correct use of mental impressions".
The same technique of impression/assent is also used, along with others, to diagnose "passions" (Greek, páthos—it's a loaded word that is used to categorize many emotions, including the debilitating ones). Thus, for the Stoics, the cause of any "passion" is an "error of judgement". What sort of error? Mistaken system of values—there's a ton more to this, but I have to skip it for brevity's sake. FWIW, some reading recommendations on this topic on a thread here[1].[1] https://news.ycombinator.com/item?id=22990579