The doctrine of promissory estoppel is an outstanding modem example of the way in which the Anglo-American legal system develops significant rules and principles out of the day-to-day decisions of our courts.

Progress in the law comes about through the formulation and acceptance of generalizations. However, merely stating the results of a number of different instances does not result in clarification and simplification. That comes only when the precedents are studied with a view to discovering the ''binding thread of principle that runs through them all." Such a principle, if discovered in the course of the appraisal of a series of cases, will make for a more ready understanding of the cases which have already been decided. Even more important, however, is the future use which can be made of the principle thus discovered. It may thereafter be employed in variant and diverse fact situations to produce workable, logical and rational solutions to problems which had previously been solved only by resort to fiction or by the use of historical anomalies and conceptual distortions. As Cohen has so aptly remarked, "A legal system that works with general principles has powerful instruments .... [A] generalized jurisprudence enlarges the law's control over the diversity of legal situations. It is like fishing with large nets instead of with single lines."