The same functional form arises as a utility function in consumer theory. For example, if there exist n types of consumption goods c_i, then aggregate consumption C could be defined using the CES aggregator:
C = left[sum_{i=1}^n a_{i}^{frac{1}{s}}c_{i}^{frac{(s-1)}{s}}
ight]^{frac{s}{(s-1)}}
Here again, the coefficients a_i are share parameters, and s is the elasticity of substitution. Therefore the consumption goods c_i are perfect substitutes when s approaches infinity and perfect complements when s approaches zero. The CES aggregator is also sometimes called the Armington aggregator, which was discussed by Armington (1969).[7]
A CES utility function is one of the cases considered by Dixit and Stiglitz in their study of optimal product diversity in a context of monopolistic competition.[8]