 Husserl is nowhere explicit about the proper method for distinguishing material ontological categories, but he does distinguish material absurdity from formal absurdity, and from the formal nonsense that marks the difference in meaning categories (1913 [2000], 523). Expressions are formally absurd if it is a priori that no object could correspond to them, based purely on formal, logical laws, without regard to which particular material concepts are employed, e.g., “a round not-round thing” is formally absurd; its absurdity would remain regardless of which adjective we substituted for ‘round’ or which noun for ‘thing’. On the other hand, expressions are materially absurd if the impossibility of there being any corresponding object is based in the particular material concepts employed, e.g., ‘a round square’ is a materially absurd expression based in the particular meanings of ‘round’ and ‘square’. Thus presumably one could attempt to distinguish material ontological categories by the material absurdity that results from substituting expressions for objects of different material kinds; ‘a round table’, for example, makes perfect sense, but if we substitute for ‘table’ a term for a geometric figure such as ‘square’ or for a day of the week such as ‘Thursday’, we get a materially absurd statement (to which it is a priori that nothing corresponds). As we will see in §2.2 below, Gilbert Ryle developed Husserl’s nonsense test for category differences in something like this way.