I do not claim that this summary criticism covers the whole ground. There are some four or five cross-correspondences which do not Obviously fall into the category described. But the details in these cases are extremely complicated, and the interpretation is not merely difficult but ambiguous. Because they are ambiguous the clue to the interpretation of these more elaborate cases must, it seems clear, he sought in the first instance in the analysis of the simpler instances of cross-correspondence; We must proceed from the simple to the complex.