“Smith’s own theory, as given in the first five editions, is for the most part a theory of moral judgement —that is to say, it is an answer to the second question set out in the initial description of the subject of philosophical ethics. […] There is no thoroughgoing inquiry of what constitutes the character of virtue, as required by the first of the two questions, even though the historical survey at the end of the book deals with both questions in turn and, as it happens, gives more space to the first topic, the character of virtue, than to the second, the nature of moral judgement.
The fact is that Smith did not reach a distinctive view on the first topic. He has a distinctive view of the content of virtue, that is to say, a view of what are the cardinal virtues; but he does not give us an explanation of what is meant by the concept of moral virtue, how it arises, how it differentiates moral excellence from other forms of human excellence. […] I think that, when Smith came to revise the work for the sixth edition, he realized that he had not dealt at all adequately with the first of the two questions, and for that reason he added the new part VI, entitled ‘Of the Character of Virtue’, to remedy the omission. It is not, in my opinion, an adequate remedy, and it certainly does not match Smith’s elaborate answer to the second question. […]
Since the second of the two topics, the nature of moral judgement, is the main subject of both versions of Smith’s book, I shall give it priority in what follows. There is in fact a clear development in Smith’s view of this topic, especially in his conception of the impartial spectator, the most important element of Smith’s ethical theory.”

The Impartial Spectator: Adam Smith's Moral Philosophy (2007), Ch. 1: Two Versions