Many people are familiar with Adam Smith’s The Wealth of Nations (WoN), But Smith’s ethical thinking was just as important. In fact, it was The Theory of Moral Sentiments (TMS), published 27 years earlier, on 12 April 1759, that made him famous.

Just The Wealth of Nations, this book marked a complete break from the thinking of the time. Ethics had until then been widely assumed to be based on God’s will (or the clerics’ interpretation of it); or something that could be deduced through abstract reason; or even something that could be felt through some ‘moral sense’ like touch or vision. 

Replacing this speculative thinking by scientific method, Smith argued instead that morality stemmed from our human nature as social beings, and our natural empathy for others. By observing ourselves and others, he said, we could discover the principles of ethical behaviour. Ethics was a matter of human psychology, stemming from how we form judgements about ourselves and others, and the influence of customs, norms and culture upon it.

This scientific approach to ethics was a sensation. It was very much in line with the Scottish Enlightenment, which sought to apply observation and scientific method to the study of human affairs. Old hierarchies were breaking down; industrialisation was eclipsing Scotland’s feudal past; radical thinkers like Francis Hutcheson and David Hume were pushing new boundaries, and religious pluralism was creating a more active debate on virtue and morality.

Smith’s book explained that morality is rooted deeply in human psychology, especially the empathy we have for our fellow humans. By our nature, we understand, and even share the feelings of others. Wanting others to like us, we strive to act such that they do. Even if there is no one else around to see how we behave, we are still impelled to act honestly, says Smith, as if an ‘impartial spectator’ is judging us all the time, setting the standard by which we rate ourselves and others. And under this imaginary eye, every choice we make helps us appreciate that standard more clearly and act more consistently in accordance with it. It is as if an invisible hand is drawing us to act in ways that promote social harmony.

TMS is mainly a descriptive account of human moral action. It examines how people actually make moral choices, and the pressures on them to do so. It also provides a guide on how we can cultivate our morality, emphasising the importance of self-reflection and self-improvement. 

Smith’s radical scientific approach in TMS and WoN provided a foundation for the subsequent development of psychology, sociology, and economics, establishing them as distinct subjects of academic enquiry. And its suggestion that self-interested actions—wanting to be liked by others, or exchanging things we value less for others’ things we value more—could produce a cooperative social and economic order, continues to have a central place in liberal thinking.

All this makes the themes in The Theory of Moral Sentiments just as relevant today as they were in 1759. Through self-reflection, we can make better moral choices. Through our empathy with others, we can foster understanding and create a more peaceful society. Through an appreciation of our shared feelings and interests, we can live and work and collaborate together for the mutual benefit of the whole of humanity.