In the Solidarity Game (Selten and Ockenfels, 1998), two "rich" persons can support a "poor" one. A strong positive correlation between one rich person's solidarity contribution and his expected contribution of the other is observed. This paper investigates the causality behind this correlation....

How can a principal (an agent) ensure that an agent (a principal) will work (pay up), if payment (work) precedes work (payment)? When a banknote is torn in two, each part is by itself worthless. A principal can pre-commit to payment-on-delivery, by tearing a banknote and giving the agent the...