1.2.4 Distribution
Let us turn now to the observations made in (2) and (3). There we observed that there are certain positions in a sentence that some words can occupy and other words cannot. Clearly, this is determined by category. This is perhaps the most basic point of word categories as far as syntax is concerned. The grammar of a language determines how we construct the expressions of the language. The grammar, however, does not refer to the individual words of the lexicon, telling us, for example, that the word cat goes in position X in expression Y. Such a system would not be able to produce an indefinite number of sentences as there would have to be such a rule for every expression of the language. Instead, the grammar defines the set of possible positions for word categories, hence allowing the construction of numerous expressions from a small number of grammatical principles. The question of how these positions are defined is mostly what this book is about, but for now, for illustrative purposes only, let us pretend that English has a rule that says that a sentence can be formed by putting a noun in front of a verb. This rule then tells us that the expressions in (15) are grammatical and those in (16) are not: