Van Cleve on the synthetic a priori

After some extensive discussions about a prioricity and analyticity with Andreas, I decided to re-read van Cleve's excellent discussion of necessity, analyticity and the a priori in Chapter 2 of Problems from Kant. One nice argument that van Cleve mentions in favour of there being synthetic a priori truths is the consideration whether the claim that all a priori truths are analytic, which the opponent of synthetic a priori truths holds, is itself analytic. He says: "What is the status of the opposing thesis that all a priori truths are analytic? It is not an empirical thesis, so if true at all, it had better be analytic. But is it? Defenders of the thesis have seldom risen to the challenge of demonstrating its own analyticity." (Problems from Kant, p. 27)