MacIntyre identifies (WJ?WR? pp. 79-81) several characteristics of an inquiry-tradition, i.e., an ongoing inquiry that on retrospective examination shows indications of progress toward a goal, that distinguish it from an inquiry in which no such progress exists.
(1) "[T]he later stages of the enquiry would have to presuppose the findings of the earlier." Naturally, this doesn't mean that the earlier findings are always confirmed, only that they are taken seriously enough that trouble is taken at later stages to identify and characterize the earlier findings in order to give the later stages something to build upon or modify.
(2) "[W]here there has been at an earlier stage unresolved and, at that stage, unresolvable disagreement, it must at some later stage be possible to provide an explanation both of why the disagreement occurred and of why it was then and with those resources unresolvable." That is, later stages provide a theory of error with which to view the problems of earlier stages.
(3) Later stages must make possible successively more adequate conceptions of the good of the inquiry. As time goes on and problems get solved, our understanding of the goal of the inquiry becomes less sketchy, thus making it possible, at least in principle, to direct the inquiry more effectively.
(4) "[T]his gradually enriched conception of the goal is a conception of what it is to have completed the enquiry."
I think this account is right; but I [don't--ed.] think it's unrestrictedly so. In particular, I think we need to distinguish between open inquiries and restricted inquiries. Restricted inquiries are structured by particular problems. It's clear that at least some such inquiries have these four properties; these are major problems that are ongoing projects. Some of these ongoing projects last for decades or even generations, some for even longer. Thus, saving the phenomena of the heavens was an ongoing research project, one that lasted quite literally millenia, which was governed by the attempt to identify the best model for capturing all the astronomical phenomena pertaining to the planets. The story of it is a well-known one, so I won't rehash it here, except to point out that the inquirers did indeed build on each others' work (1), develop error theories for previous limitations (2), filled out their understanding of what it was they were actually doing (3), and in so doing began to have a better idea of what it would be to complete the inquiry (4).
However, there is another type of inquiry, and that is the open inquiry, the kind that is not tied down to any particular problem. Physics, for instance, is an open inquiry of this sort. And the application of (4) becomes very tricky here, because it seems at first glance that it's inimical to open inquiry for there to be any conception of completion. MacIntyre will later recognize something like this problem when he discusses the difference between tradition-constituted inquiry and Hegelian inquiry. Here's what he says there (WJ?WR? 360-361):
Implicit in the rationality of such enquiry there is indeed a conception of a final truth, that is to say, a relationship of the mind to its objects which would be wholly adequate in respect of the capacities of that mind. But any conception of that state as one in which the mind could by its own powers know itself as thus adequately informed is ruled out; the Absolute Knowledge of the Hegelian system is from this tradition-constituted standpoint a chimaera. No one at any stage can ever rule out the future possibility of their present beliefs and judgments being shown to be inadequate in a variety of ways.
I'm not sure that this quite says everything that needs to be said with regard to the problem, but it points immediately to the chief concern of (4), which is that of a theory of truth. Just as a progressive inquiry needs a theory of error with regard to which it can evaluate the limitations of prior approaches, it needs a theory of truth with regard to which it can evaluate its own adequacy (within whatever limitations to which it is subject at that point in time). MacIntyre tends to understand this theory of truth as "a conception of what it would be to understand things as they are absolutely," which in turn he complete understanding of the subject-matter. I think it's here that he goes slightly wrong, because it's clear that open inquiries can be progressive inquiries directed toward a goal without that goal being the complete understanding of the subject matter. We do need a "conception of what it would be to understand things as they are absolutely", but this is very different from having the conception of a complete understanding of the subject matter, or, at least, it would only be the same within particular traditions of inquiry. Rather, again, what is really relevant here is a theory of truth or, if you prefer, understanding: the inquiry needs not a conception of complete understanding but a conception of genuine understanding; and we need not a conception of the understanding of the complete subject matter, but a theory of understanding that is completely adequate to the thing in itself insofar as it is able to be understood by the mind's capacities for understanding.
MacIntyre does recognize that open inquiries exist; he tends to characterize them as being such that our conception of what it would be to have a complete understanding of the subject matter exhibits that complete understanding as unattainable -- presumably in practice by us, because we can only conceive of a complete understanding as something at least in principle obtainable by some capacity to understanding. I do not think that this is enough. One of my reasons for thinking so is something that MacIntyre himself hints out but does not draw out fully enough, namely, that this theory of truth or of understanding may itself be one of the things changing and in dispute in the course of the inquiry. Obviously, insofar as the disputants are participating in the same inquiry, there will always be something shared; but the theory of truth or understanding will itself be progressing in a progressive open inquiry. What will be progressing, however, will not be a conception of what it would be to attain the complete subject matter (even if it is not in practice attainable) but a conception of the ways the subject matter can be understood, the modes in which the object of inquiry presents itself to inquirers. This is not the same as a conception of what it would take to complete the inquiry, but only of the way inquiry can be evaluated in terms of its effectiveness for understanding the object of inquiry.
* All page numbers will refer to Alasdair MacIntyre, Whose Justice? Which Rationality?, U Notre Dame P (Notre Dame, Indiana: 1988).