We have looked at the role played by categories in characterizing the grammatical properties of words. In §2.2, we looked at the criteria used for categorizing words, noting that semantic criteria have to be used with care, and that morphological criteria (relating to the inflectional and derivational properties of words) and syntactic criteria (relating to the range of positions which words can occupy within phrases and sentences) tend to be more reliable. In §2.3 we suggested that we can determine the categorial status of a word from its morphological and syntactic properties, with substitution being used as a test in problematic cases. In §2.4 we went on to draw a distinction between substantive/lexical categories (whose members have substantive lexical content) and functional categories (whose members have no substantive lexical content and serve only to mark grammatical properties such as number, person, case etc.). We then looked at a number of different types of functional category found in English. We began in §2.5 with determiners (= D) and quantifiers (= Q), arguing that they are categorially distinct from adjectives since they precede (but don’t follow) adjectives, they can’t be stacked, and they impose grammatical restrictions on the types of expression they can modify (e.g. a can only modify a singular count noun expression). In §2.6, we looked at pronouns and argued that English has at least three distinct types of pronoun, namely N-pronouns (like one), Q-pronouns (like several) and D-pronouns (like this). We went on to note that recent research has suggested that personal pronouns like he are also D-pronouns, but that this categorization is not entirely unproblematic. In §2.7 we looked at the functional counterparts of verbs, namely auxiliaries: we argued that these are functors in that (unlike lexical verbs) they describe no specific action or event, but rather encode verb-related grammatical properties such as tense, mood, voice and aspect; we noted that auxiliaries are syntactically distinct from verbs in that (e.g.) they undergo inversion. In §2.8 we discussed the nature of infinitival to: we showed that it is distinct from the preposition to, and shares a number of properties in common with finite auxiliaries (e.g. auxiliaries and infinitival to allow ellipsis of their complements, but prepositional to does not). We noted the assumption made in much research over the past three decades that finite auxiliaries and infinitival to are different exponents of the same category (labelled I/INFL/Inflection in earlier work and T/Tense-marker in more recent work), with an auxiliary like will marking finite tense, and infinitival to marking non-finite tense. In §2.9 we argued that complementisers (= C or COMP) like that/if/for are a further category of functors, and that they mark the force of a complement clause (e.g. indicate whether it is interrogative, declarative or irrealis), and that (e.g.) if is distinct from interrogative adverbs like how/when/whether in that it can only introduce a finite clause, and cannot introduce a clause which is used as the complement of a preposition. In §2.10, we showed how the labelled bracketing technique can be used to categorize words in particular phrases and sentences. Finally, in §2.11 we noted that assigning words to grammatical categories provides a description of only some of their grammatical properties, and that a fuller description requires the use of grammatical features to describe their other grammatical properties. We went on to note Chomsky’s claim that the categorial properties of words can also be described in terms of a set of grammatical features – bringing us to the conclusion that all grammatical properties of words can be characterized in terms of sets of features.