A good way to understand the idea of a social contract is to think about different sorts of obligation. What can make it the case that I am morally obliged to perform an activity?

Take the case of a dutiful son, who looks after his aged and infirm parents. Why is it that the son is obliged to do so? One answer is that the obligation simply flows from the nature of the parent/child relationship – so that the obligation is just a natural one. The obligation is – it could be said – just ‘hardwired’ into the parent child relationship. On one account, it’s hardwired in by the person who determines all the hardwiring that goes to make us how we are – God. But whatever its source, this explanation amounts to an account of natural obligations.

There is another way of placing oneself under an obligation. Suppose I ask to borrow some money from a colleague. She agrees, if I pay her back, and so I say ‘I’ll pay you back that tenner next week.’ Then – clever philosophical tricks aside – I am under an obligation to pay back the money next week. Here, I am under an obligation because I have voluntarily put myself in that position, by making a promise to the person who lends me the money. This is a contractual obligation.

So there are two bases for obligation. Now, let’s shift the terrain slightly, by asking what makes it the case that I should obey the government? (This is a version of the question – what makes government legitimate?) Obviously, there can be three answers to that question – our obligation to obey the government might be a natural obligation, a contractual obligation, or might not exist at all. Historically, the fight has been between the first two of these – nowadays the main debate is between the last two.

Amongst those to argue for ...