 Few nowadays look for Cartesian certitude in mathematics, so Carnap’s position here may seem reasonable. It is not so clear, however, that he has answered the problem of applicability. Even if a conservative extension result can only be given in a more powerful system, we need the result to be a contentful truth, not just a string of symbols we can derive from some system, if we are to have reassurance that a particular calculus we are about to use in designing bridges or computers will be pragmatically useful. And if the Carnapian grants that the result is a contentful truth, we can ask what, according to this formalistic position, constitutes that truth. Carnap, to be sure, was motivated by a horror of becoming embroiled in metaphysical disputation. But if his standpoint is emptied not only of epistemological ambition but is so deflationistic as to say little more than that metamathematical techniques can be applied to formalisations of mathematical and scientific theories then it is also emptied of all philosophical interest and ceases to make an intervention in the debates in philosophy of mathematics.