An appreciation of temporal and logical relationships is one of the essential and defining features of human cognition. A central question in developmental psy chology, and in the philosophical speculations out of which psychology evolved, has been how children come to understand temporal and logical relationships. For many recent investigators, this question has been translated into empiri cal studies of children's acquisition of relational terms-words such as before, after, because, so, if, but, and or that permit the linguistic expression of logi cal relationships. In the mid 1970s,...