"Differences of practice are of two kinds: those that (after the initial surprise) we can accommodate as mere divergences of custom or of culture, and those that strike us as reflecting differences of principle. The distinction is prior to the formulation of the underlying principle. We apprehend a divergence of practice from our own either as merely a different way of practising the same religion, even if not to our own taste, or else as signalling that the religion of those who observe the divergent practice is not quite the same as our own: and, in the latter case, we ordinarily recognize the divergence as being of the second kind before we can put into words the difference of principle that we feel to exist. If you do this, or if you do not do that, we want to say, you must understand what you are doing in an essentially different way from that in which we understand it; recognizing this to be so does not require that we have any means at hand to formulate that difference of understanding. It is in this that we see most clearly reflected the priority of practice over doctrine that usually prevails: the doctrine attempts to give verbal expression to a significance that is apprehended in advance of that expression. That is why differences of practice, when they are of the second kind, are of greater importance than differences of formulated doctrine."
Michael Dummett, "The intelligibility of eucharistic doctrine," in The rationality of religious belief: essays in honour of Basil Mitchell, ed. William J. Abraham and Steven W. Holtzer (Oxford: Clarendon Press, 1987), 236-237.