We show how a treebank can be used to cluster words on the basis of their syntactic behavior. The resulting clusters represent distinct types of behavior with much more precision than parts of speech. As an example we show how prepositions can be automatically subdivided by their syntactic behavior and discuss the appropriateness of such a subdivision. Applications of this work are also discussed. 1 Introduction The construction of classes of words, or calculation of distances between words, has frequently drawn the interest of researchers in natural language processing. Many of these studies aimed at finding classes based on co-occurrences, often combined with the aim of establishing semantic similarity between words (McMahon and Smith, 1996; Brown et al., 1992; Dagan, Markus, and Markovitch, 1993; Dagan, Pereira, and Lee, 1994; Pereira and Tishby, 1992; Grefenstette, 1992). We suggest a method for clustering words purely on the basis of syntactic behavior. We show how the necessary...