Presuppositionalist Metaphysics holds that first principles should be discovered or known prior to developing an empirical method of inquiry. This is a time-honored philosophy that is still held by apologists the world over. In staunch contrast to presuppositionalism, logical positivists and pragmatists often seek, instead, to take the functionality of the empirical method as self-evident, and then infer ontological and cognitive stability from that. This is an effort, in both cases, to dispense with metaphysics in favor of the materialistic philosophy espoused by thinkers such as A. J. Ayer, Rudolf Carnap and the early Wittgenstein. This method can be subjected to two critiques: 1) We are still engaging in presuppositionalism since we're now presupposing that science works or 2) This is circular reasoning because the goal is to find an ontological structure in the world which will allow materialistic methods to work by assuming that the materialistic methods work.
Because apologists are often more careful in their philosophy, presuppositionalist metaphysics (being the only logical course of investigation in metaphysics) can then be used to infer a designer. If first principles are obtained, then we have either obtained them by divine inspiration, or by our own investigation. But to find them by our own investigation would require a functional method of empirical inquiry, which we cannot have without the first principles from which we might infer the appropriate method of empirical inquiry. So, if we are to have a functional empirical method, we must possess the first principles a priori — thus they have been given to us by God. This is why creationists will often challenge Darwinists on epistemological grounds -- the Darwinists have rigged the game by simply "defining away" the first principles which make knowledge possible while, for creationists, the methodology is based on the principles given by divine writ.