We characterize quasi-orderings on the power set of a set of alterativ
es. The subsets to be ranked are interpreted as opportunity sets avail
able to an individual. The main criteria for ranking these opportunity
sets are the individual preferences on the universal set of alterativ
es itself, and the freedom of choice associated with each subset of th
e universal set. This is reflected in the axioms used in the character
izations. (C) 1994 Academic Press, Inc.