Ernst Cassirer offered interesting comments to Kantian distinction between analytic and synthetic propositions. His interpretation is instructive, because it does not pretend to present Kant's thought most accurately but shows its development in time. Cassirer highlights the differences between the first edition of the 'Critique of Pure Reason' and the 'Prolegomena'. It is in this latter work that Kant introduces a distinction between observational and experiential statements. This distinction has led Cassirer to formulate a number of new insights about how Kant should be understood. He used these insights to put together a new theory of concept construction. Its full exposition has been given in 'Substanzbegriff und Funktionsbegriff'.