One word was omitted from 1380 sentences in a way that yielded 3 treatments of sentence length, within which were 4 treatments of position of omission, within which were 6 treatments of word class of the omitted word. The length, distribution, and grammatical structure of context are all independently effective sources of constraint on words in sentences. The predictability of words belonging to a given class is inversely related to the size of that class. Several other results are also noted. (PsycINFO Database Record (c) 2006 APA, all rights reserved)