Money is just a promise. It is a formalisation of "Bill, here's a pig, owe me one". Then Fred does some work for you and you say to Bill "don't owe me, owe Fre

Money is just a promise. It is a formalisation of "Bill, here's a pig, owe me one". Then Fred does some work for you and you say to Bill "don't owe me, owe Fred". Humans know who they owe and who owes them. We write it down when society gets too big to hold all the people we might owe in our collective heads.