 At the end of our discussion in section 1 above we saw that there is a serious difficulty in understanding what Kant intends here—a difficulty to which he himself explicitly calls attention. Kant does not think that the particular causal law that “the sun is through its light the cause of heat” is itself a synthetic a priori truth. Indeed, the very same difficulty is present in our discussion at the beginning of this section. For, what Kant is saying in § II of the second edition of the Introduction to the Critique is that necessity and strict universality are “secure criteria of an a priori cognition” (B4; emphasis added). More specifically (B3): 