  5. However, if the transcendental claims involved are not a matter of merely causal or natural necessity, this then raises the question of what form of necessity they do in fact involve. If they were true in virtue of their meaning alone (even if unobviously so), and thus analytic, then the necessity might be said to be purely logical, where to deny the claim is then to assert some form of logical contradiction (cf. Bennett 1979, Walker 1978: 18–23, Walker 1989: 63–4, Bell 1999). However, this may not seem to be the case in many instances of such transcendental claims, where in fact they may be said to be synthetic a priori (cf. Wilkerson 1976: 199–213), while the whole analytic/synthetic distinction is itself fraught with difficulty. To many, nonetheless, it has appeared that the transcendental claim is not a logical necessity, but stands somewhere between that and natural necessity, perhaps putting it into the camp of metaphysical necessity, as this is sometimes understood: that is, a necessary relation which holds not by virtue of logical or causal constraints on the nature of logical or physical possibilities, but by virtue of metaphysical constraints on how things can be—much as the fact that nothing can be red and green all over is arguably not determined by any law of logic or causal law, but the nature of colour, and how it can be exemplified in things.