In his writing, Smith demonstrates how important realism and absence of prejudice is to him. He doesn't depict people in a better light than they deserve, and he also doesn't make them more evil than they are. In both his major works, Smith starts from the rather noncontroversial idea that man simply acts purposefully and is better placed to decide for himself than any other person or entity. In the Theory of Moral Sentiments, he also makes one essential psychological assumption: we are naturally endowed with a capacity to share and understand another person's emotions and feelings, that is, with a capacity for empathy (in the language of his time, he uses the word "sympathy"). "How selfish soever man may be supposed, there are evidently some principles in his nature, which interest him in the fortune of others, and render their happiness necessary to him, though he derives nothing from it except the pleasure of seeing it."

Smith also believes that everybody naturally aims at pleasing others. "Nature, when she formed man for society, endowed him with an original desire to please, and an original aversion to offend his brethren. She taught him to feel pleasure in their favourable, and pain in their unfavourable regard." Even more, we want to make sure we deserve a positive verdict. We actively educate ourselves so that we can hope to be truly praiseworthy. In Smith's ingenious thought experiment, we do that by relying on a fictitious "impartial spectator" - who is nothing else but our own conscience.

It is no coincidence and no misnomer that the title of the book mentions "moral sentiments". Smith is not interested in reason, but in feelings, or sentiments, as a source of knowledge about moral propriety. It is through the immediate reaction of others that we recognise or feel what is good and virtuous, through the reciprocity that we are granted or denied, and through our own "impartial spectator's" praise or reprimand. Of course, the "impartial spectator" knows only as much as we do ourselves. The relevant difference is, however, that the "impartial spectator" is able to step back a little, to refrain from short-term calculations, and to reflect soberly. It is he who confronts impulses, sentiments and feelings with rationality. For this, we are required to be capable of imagination and sympathy: we need to put ourselves in someone else's shoes. We must imagine how someone else would look at us - not if that someone else was in our own position, with our own baggage and environment, but with the position, experience and environment proper to that someone else.