AbstractThe automatic paraphrasing system used in the experiments described herein consisted of a phrase structure, grammatically correct nonsense generator coupled with a monitoring system that required the dependency relations of the sentence in production to be in harmony with those of a source text. The output sentences also appeared to be logically consistent with the content of that source. Dependency was treated as a binary relation, transitive except across most verbs and prepositions. Five experiments in paraphrasing were performed with this basic system. The first attempted to paraphrase without the operation of the dependency monitoring system, yielding grammatically correct nonsense. The second experiment included the operation of the monitoring system and yielded logically consistent paraphrases of the source text. The third and fourth experiments demanded that the monitoring system permit the production of only those sentences whose dependency relations were non-existent in the source text. While these latter outputs were seemingly nonsensical, they bore a special logical relationship to the source. The fifth experiment demanded that the monitoring system permit the production of sentences whose dependency relations were the converse of those in the source. This restriction was equivalent to turning the dependency tree of the source text upside down. The output of this experiment consisted only of kernel type sentences which, if read backwards, were logically consistent with the source. The results of these experiments determine some formal properties of dependency and engender some comments about the role of dependency in phrase structure and transformational models of language.