Structural categories of grammar (such as clitic, affix, compound, adjective, pronoun, dative, subject, passive, diphthong, coronal) have to be posited by linguists and by children during acquisition. This would be easier if they simply had to choose from a list of pre-established categories. However, existing proposals for what such a list might be are still heavily based on the Latin and English grammatical tradition. Thus, descriptive linguists still have no choice but to adopt the Boasian approach of positing special language-particular categories for each language. Theorists often resist it, but the cross-linguistic evidence is not converging on a smallish set of possibly innate categories. On the contrary, almost every newly described language presents us with some "crazy" new category that hardly fits existing taxonomies. Although there is thus no good evidence for pre-established categories, linguists still often engage in category-assignment controversies such as Is the Tagalog ang-phrase a subject or a topic? Is German er a pronoun or a determiner? Are Mandarin Chinese property words adjectives or verbs? Is the Romanian definite article a clitic or a suffix? A consequence of the non-existence of pre-established categories for language description is that such questions are pointless. Instead of fitting observed phenomena into the mould of currently popular categories, the linguist's job is to describe the phenomena in as much detail as possible. A consequence of the non-existence of pre-established categories for typology is that comparison cannot be category-based, but must be substance-based, because substance (unlike categories) is universal. This has been recognized in the Greenbergian approach, though it is often hidden by widely practiced terminology ("noun-genitive" order, "verb-object" order, etc.).