Ordinal utility theory permits only those assumptions on utility functions that are preserved under increasing transformations. The rationale for this rule is that any assumption P not preserved under increasing transformations cannot be verified with observations of choice behavior: if a utility u satisfies P, there will exist another utility uЈ that does not satisfy P but that represents the same preferences as u. Nonordinal assumptions therefore seem to be needlessly restrictive: given a nonordinal assumption, one may always make a weaker assumption with the same implications for choice behavior. According to this view, the only role for cardinal utility is the normative one of representing interpersonal comparisons of utility.Ordinalism's first targets were diminishing marginal utility (DMU) and concavity, which had long served as arguments for why consumer preferences should be convex. Neither DMU nor concavity is preserved by increasing transformations and hence neither is an ordinal assumption. The pioneer ordinalists such as Kenneth Arrow (1951) claimed that diminishing marginal utility is tantamount to assuming that utility is cardinal. Arrow's position remains predominant: either an assumption on utility is ordinal or it is cardinal (see, e.g., Andreu Mas-Colell et al., 1995, chap. 1). This paper will take sets of utility functionswhich we call psychologies-as primitive; this will define a finer gradation of properties of utility that allows for intermediate standards of measurement. In this framework, ordinal utility theory takes the psychology consisting of all increasing transformations of any given utility function as primitive and lies at one end of the measurement spectrum.1 Cardinal utility theory takes the psychology consisting of all increasing affine transformations of a given utility as primitive; since this is a smaller set of utility functions, cardinality is a stronger (more restrictive) theory than ordinality. Ratio scales which take still smaller psychologies as primitive (the functions generated by all increasing linear transformations) are also common, particularly outside of economics. But in addition to these well-known measurement scales, there is an infinity of intermediate cases. Diminishing marginal utility and concavity lie precisely in the middle ground between cardinality and ordinality. The psychology consisting of all concave utility representations of a given preference relation is larger than any cardinal psychology it intersects, but smaller than any ordinal psychology it intersects. Concavity thus presupposes an intermediate standard of measurement and does not deserve its strongly nonordinalist reputation. Compared to a cardinal psychology, a concave psychology is easier to assemble in that an agent does not have to make as many utility