This paper provides an exposition of the standard model of economic choice, applying Popper's method of rational reconstruction. It emphasizes that the explanation of downward-sloping demand curve, which is the original explicandum of this model, does not entail explanation of choice as such. Two alternative variants of the model of are considered: one based on the notion of diminishing marginal utility and the other on the concept of ordinal utility. Each variant is understood as a tentative solution to a theoretical problem and clarifies why the former is replaced by the latter. It also shows how the latter relates to consumer preferences and choices and why choices remain unexplained by the model.