words to be encountered during tile text processing. More recently, a straight dietionalT approach has been supplemented througtl the use of computational decision procedures. The present paper reports on one such computational system, WISSYN, in which decisions about how to code certain words are based on conditional probabilities of various form classes occurring in given syntactic environments. A computer program is described which will assign each word in an English text to its form class or part of speech. The program operates at relatively high speed in only a limited storage space. About half of the word-events in a corpus are identified through the use of a small dictionary of function words and frequently occurring lexical words. Some suffix tests and Iogical-decislon rules are employed to code additional words. Finally, the remaining words are assigned to one class or another on the basis of the most probable form classes to occur within the already identified contexts. The conditional probabilities used as a basis for this coding were empirically derived from a separate hand-coded corpus. On preliminary trials, the accuracy of the coder was 91% to 93%, with obvious ways of improving the algorithm being suggested by an analysis of the results.