Full Idea
Despite a tendency to read consent into moral claims, it is hard to make sense of our morality without acknowledging the independent weight of reciprocity. If my wife is unfaithful I have two different grounds of outrage: our promise, and my loyalty.
Gist of Idea
Moral contracts involve both consent and reciprocity; making the deal, and keeping it
Source
Michael J. Sandel (Justice: What's the right thing to do? [2009], 06)
Book Reference
Sandel,Michael J.: 'Justice: what's the right thing to do?' [Penguin 2010], p.149
A Reaction
The point is that Hobbes and co over-simplify what a contract is. Compare a contract with a promise. One must be two-sided, the other can be one-sided.