The favourable reception of both books is all the more remarkable because their subjects are different and on the surface, at least disjunctive, if not contradictory. The animating spirit of The Wealth of Nations is "interest" or "self-love"; that of The Theory of Moral Sentiments is "sympathy" or "fellow-feeling". The memorable dictum that highlights the contrast between the two appears early in The Wealth of Nations: "It is not from the benevolence of the butcher, the brewer, or the baker, that we expect our dinner, but from their regard to their own interest." This sentence is often quoted out of context. The preceding passage is less stark — indeed, it might well have appeared in the earlier book:
In civilised society, he [man] stands at all times in need of the cooperation and assistance of great multitudes . . . In almost every other race of animals, each individual, when it is grown up to maturity, is entirely independent, and in its natural state has occasion for the assistance of no other living creature. But man has almost constant occasion for the help of his brethren, and it is in vain for him to expect it from their benevolence only.
Only then, after placing man firmly in society, dependent on the "cooperation" and "help of his brethren," does Smith invoke the idea of interest — not to deny the idea of benevolence, but rather to supplement "benevolence only" by another more dependable idea. The butcher, brewer, and baker are appealed to on the basis of their interests, because that would be more effective to achieve the same end — the good of others, their "brethren".
Another memorable phrase, the "invisible hand", is often cited as the attempt to reconcile self-love and the public good. By engaging in industry, man "intends only his own security . . . [and] his own gain, and he is in this, as in many other cases, led by an invisible hand to promote an end which was no part of his intention. . . By pursuing his own interest he frequently promotes that of the society more effectually than when he really intends to promote it." This phrase appears only once in The Wealth of Nations, late in the book, as well as in Moral Sentiments in quite a different context. There the issue is not industry but luxury, the disparity between the rich and the poor.
In spite of their natural selfishness and rapacity, though they [the rich] mean only their own convenience, though the sole end which they propose from the labours of all the thousands whom they employ, be the gratification of their own vain and insatiable desires, they divide with the poor the produce of all their improvements. They are led by an invisible hand to make nearly the same distribution of the necessaries of life, which would have been made, had the earth been divided into equal portions among all its inhabitants, and thus without intending it, without knowing it, advance the interest of society, and afford means to the multiplication of the species.