This paper argues that default plays an important positive role in the
economy. If markets are incomplete and traders are only able to enter
into contracts that they will be able to execute regardless of future
events, contingent contracting may be severely restricted. Moreover,
opening new markets may not relieve these restrictions. Default promot
es efficiency in a way that opening new markets does not, by making it
possible for traders to enter into contracts that they will be able t
o execute with high probability, but not with certainty.