Hurley: A Partial Overview

Self-love, Smith suggests, is pleasure in one's own good fortune.

Sympathy, by contrast, is pleasure in the fortunes of others. (ch i)

In the case of sympathy, I experience pleasure, but only if, and because, of some benefit to you, and I experience pain, but only if, and because, of some suffering by you.

Mutual sympathy, people sharing your grief, or outrage, or joy, or resentment, is one of the great sources of happiness for people (ch II)

To be in sympathetic accord, whether with someone's passion, or their opinion, or their taste, just is to admit the reasonableness of the passion, opinion, or taste (ch III)

But in the case of judgments of opinion and judgments of taste we can both adopt the same perspective towards a painting or a scientific observation, whereas in the case of passions your grief is distinctively yours, my resentment is distinctively mine, etc.  How can we enter into alignment with such passions, given that we cannot in the same way adopt the same perspective towards them (e.g. my perspective towards my passion and the cause of it is fundamentally different than your perspective towards my passion and the cause of it)? (ch IV)

The answer is that we learn to adjust our passions to reflect the standpoint of the impartial spectator.  I tone down my grief or my hatred or my resentment, for example, so that it is at a level you can enter into, and you sensitize yourself to the grief, hatred, or resentment of others, so that you can enter into their grief, resentment, etc. when it is suitably toned down.  This adjustment to the standpoint of the "impartial spectator" establishes when grief, or  resentment, or joy, or kindness is an appropriate response to the appropriate degree.  This appropriate response is the reasonable, virtuous response.

The people who have adjusted their passions to the standpoint of the impartial spectator, e.g. who only experience resentment when it is appropriate to do so, and to the appropriate extent, are characterized as having the relevant virtues.  The person who adjusts her bodily appetites to the standpoint of the impartial spectator is prudent, and temperate, the person who adjusts his resentment to the standpoint of the impartial spectator is just, etc. (ch V)

The key distinction between passions, and virtues, is between the amiable virtues that manifest the requisite experience of the social passions, and the respectable virtues, many of which manifest the requisite experience of the unsocial passions.  Beneficence and kindness are amiable virtues that manifest appropriate experiences of the relevant social passions; justice is a respectable virtue that manifests appropriate experience of the relevant unsocial passion, resentment. (Sec. II, Chs III and IV)

The main difference between the two kinds of passions is that in the case of a social passion and the corresponding amiable virtue, say kindness, the impartial spectator can sympathize with both the kind person and the person who benefits from their kindness, whereas in the case of the unsocial passions and respectable virtues, say resentment (the passion) and justice (excellence in the appropriate experience of resentment), if I sympathize with the resenter I join in resenting the resentee, and if I sympathize with the resentee I must judge the resenter's passion to be inappropriate ("He didn't do anything wrong."  "You are completely overreacting!").  Unsocial passions force the spectator to take sides; social passions do not.

Two interesting points: 

First, the excellent person is the person who does a better job of occupying the standpoint of the impartial spectator, whether in opinion, taste, or judgement.  When such a person experiences a painting as beautiful, it is, when they experience a proton going through a cloud chamber, that's what's happening, and when they experience an action as an act of kindness or of injustice, it is. 

Second, "hence it is, that to feel much for others, and little for ourselves, that to restrain our selfish, and to indulge our benevolent, affections, constitutes the perfection of human nature." (20)  This unselfish person will be the happiest person, capable of trusting relationships and meaningful commitments in a way that the selfish person is not.  Not the standard picture of Adam Smith, and not the standard account of reason attributed to Adam Smith.