With preference changes, cardinal utility is indispensable. For any necessity good, there exists an intermediate consumption level at which a change in preference intensity has no effect on utility, below/above which an increase in preference intensity decreases/increases utility. This is supported by an indicative empirical survey. At the intermediate consumption level, the utility from the relevant good is zero. For a Cobb-Douglas utility function, this intermediate consumption level equals one, making the choice of the unit of measurement non-arbitrary.