Adam Smith's theory of justice seems sketchy and anaemic to modern eyes. It is often described as 'thin' because it included only three rules of justice that must be guaranteed by law:
A thin concept of justice is limited to the bare bones of basic rights that are needed for society to function cooperatively and make progress. Thus the classical liberal theory of justice offers no particular remedy against encountering people who disagree with you or have a different vision of the purpose of life. Under Smith’s theory of justice, failing to meet somebody else’s moral standards is not a matter falling within the purview of law and the state, so we could shun and avoid or boycott such nefarious characters, but we wouldn't be able to call the police to come and cart them off to prison.
In Smith’s vision there are no state-backed guarantees concerning wealth redistribution and equalisation. If some people wind up richer than others there is no theory of justice that supports levelling them down. They must be left to the dictates of their own conscience in relation to their charitable contributions, and if they chose not to share nicely with the poor that would be the end of that. As long as they don’t attack other people or try to cause them harm, the law would just leave them to get on with it.
In this universe, whether you're rich or poor is a matter of concern only to yourself and your friends and family. Even if you're the CEO of a large corporation, there would be no law saying that you have to disclose to members of the public exactly how much money you earn, so that we can all decide whether it's fair, whether you "deserve" your wage, and whether you're "worth it".
The classical liberal concept of justice is described as being ‘thin’ because it leaves out so many things that we expect these days, especially the right to decide how much money other people should have. It offers only a ‘negative’ conception of justice because it only dictates what you must not do: not kill, not steal, not bear false witness, etc. A negative conception of justice contains no positive edicts: it doesn’t try to force everyone to do anything in particular. So, ‘sell all you have and give the money to the poor’ is merely advice on what you could do to become a better person, not a commandment concerning something you must do by law in order to avoid being thrown in the slammer.
A thin concept of justice allows people to make up their own minds about what they want to do, and leaves them free to get on with it, as long as they don't steal other people's stuff, cheat, or hurt anyone else.
A legal system based on this type of negative theory of justice clearly fails to meet modern expectations of social justice. Today, social justice generally works the opposite way: we create a wish list of how the world should ideally look, and then force other people to abide by it. This is achieved by identifying the moral obligations that should be incorporated into our theory of justice.
The benefits of Smithian justice
Smithian justice has little to say about your personal morality (and how to force other people to abide by your personal code of justice) because it focuses on the moral framework underpinning interactions with people who are neither your close friends nor your family, and whose private morality should therefore be none of your business, really. The moral code required to get along with other human beings you encounter in daily life is not the same as the moral code that binds you to your family and friends. Your family and friends should agree with your vision of life, but you can cooperate with other human beings around you without any need for them to share your vision of life. The level of trust required for markets to function is indeed 'thinner' than the level of trust required between friends and lovers.
Time and experience have shown that the greater the scope for free markets, the greater the sense of trust and community in the thin sense. No society can function or be successful when everyone is busy stealing and cheating and stabbing each other in the back.
In public, people will always cooperate with each other, keep their promises, and try to do the right thing by each other whenever possible, so that we can all get on with the private business of going about our lives and being happy with our friends and family.
The so-called ‘thin’ concept of justice turns out not to be so thin after all. It seems flimsy at first glance, by comparison to the levels of trust we expect in our private family space, but over time it surprises us by expanding beyond all measure the scope of freedom, cooperation, trust, and prosperity.
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