Anything that David Konstan writes, I read with great interest. He has a review now in BMCR of Simo Knuuttila, Emotions in Ancient and Medieval Philosophy (Oxford, 2004): see it here. Konstan's general judgment is that, for classical and medieval thought, Knuuttila's book is now the most thorough and comprehensive handbook on the emotions. But Konstan finds the book weak on analysis and, especially, he thinks that Knuuttila is insufficiently sensitive to deep discontinuities of thought which might underlie superficial or verbal agreement. For instance:
There is no doubt that mediaeval Christian thinkers were deeply indebted to classical discussions of the soul and its faculties, and K. sets out the lines of descent clearly, including the role of Avicenna and other Arab scholars in transmitting ancient views. Perhaps the greatest question concerning the continuity of the ancient and mediaeval traditions, however, derives from the Christian focus on sin. From this perspective, appetites are like any other impulse, whether pleasures and pains or love for our fellow creatures, that distract a person from the love of God. Thus, K. writes of Augustine: "Augustine's description of the different philosophical theories of the emotions is not very satisfactory... Augustine's own view is compatible with the Platonic distinction between an emotional and a rational part of the soul, but he is more interested in conceptualizing emotional matters by means of the concept of will, which was also central in his theology of sin" (160). K. observes that the role of the will is new in Augustine, although he adds: "The tasks of the will are not, however, very different from that given to the dominant part of the soul by later Platonists" (168). But the connection with sin invites a radically new approach to the whole question of the emotions, which may not lend itself so easily to a chronological survey.
Augustine introduces specifically Christian affects, such as love of God, that pertain to the highest part of the soul. K. explains that "The feelings which are immediately associated with these attitudes differ from the movements which Augustine calls passions," and he adds that, besides these religious emotions, "Christians can have non-standard mystical experiences and feelings" (161). Here again, I found myself wondering whether, despite some terminological overlap, we are really in the same world as classical theories of the emotions, even if there are reminiscences here and there of Plotinus.
But here is a difficulty for Konstan's concern. Either sin exists, or it does not. Either human nature exists, or it does not. Suppose human nature exists, but sin does not exist. Then whether Augustine or others believed that there was such a thing as sin, would make no difference to what the emotions in fact are, or to what emotions were for Augustine (how they arose within him, how they affected him). The best approach to interpreting Augustine, then, would be to take him to be describing and talking about the same emotions that everyone else has and which those who don't believe in sin were trying to describe.