Fig. 91 Indifference curve.
A combination of OA units of product X, and OB units of product Y, yields exactly as much satisfaction to the consumer as does the combination of OC units of product X and OD units of product Y.
Indifference curves always slope downwards because, rationally, consumers will always prefer more of both products and so would not be indifferent between two combinations of products where one combination offers more of both. Specifically, they would only give up one product if they receive more of another for it, being indifferent as between combination E, which offers a lot of product X and little of product Y, and combination F which offers less product X and more product Y (see ECONOMIC MAN).