Impartiality through ‘Moral Optics’: Why Adam Smith revised David Hume's Moral Sentimentalism

We read Adam Smith's Theory of Moral Sentiments as a critical response to David Hume's moral theory. While both share a commitment to moral sentimentalism, they propose different ways of meeting its main challenge, that is, explaining how judgments informed by (partial) sentiments can nevertheless have a justified claim to general authority. This difference is particularly manifest in their respective accounts of ‘moral optics’, or the way they rely on the analogy between perceptual and moral judgments. According to Hume, making perceptual and moral judgments requires focusing on frequently co-occurring impressions (perceptions of objects or reactive sentiments) for tracking an existing object with its perceptual properties or an agent's character traits. Smith uses visual perception for the purpose of illustrating one source of the partiality of the sentiments people feel in response to actions. Before making a moral judgment, people have to disregard this partiality and accept that they are all equally important. Smith and Hume's different ways of relying on the same analogy reveals the still-overlooked and yet profound differences between their moral theories.