 Husserl provides an extensive discussion of categories of meaning in the Logical Investigations, arguing that differences in categories of meaning (which seem to be more like syntactic than semantic categories) can be distinguished by noting where nonsense results from substituting one term for another. E.g., in the sentence “This tree is green” we may substitute “chair” – but not “careless” – for “tree” without turning sense into nonsense, marking the difference between the meaning categories of nominative material and adjectival material (1913 [2000], 511–512). Husserl’s understanding of ‘nonsense’ is rather strict: he counts only those strings of words that are syntactically incorrect (so that they form a mere ‘heap of words’ and cannot be combined into any unified meaning (Husserl 1913 [2000], 522)) as strictly nonsensical, and thus as signs of differences in categories of meaning. (Husserl repeatedly distinguishes the nonsense of verbal formations like “a round or” (in which no unified meaning emerges) from cases of mere absurdity such as “a round square”, in which the expression has a unified meaning, although it is a priori that no object can correspond to the expression (1913 [2000], 516–17)).