Anglican comprehensiveness, extolled variously as a virtue among some Episcopalians reluctant to abet schism, has come under fire of late as actually--despite promising appearances--incoherent. Crudely put, comprehensiveness refers to the quality of keeping divergent theological parties in communion such that they may worship together. In Anglicanism, ideally, Anglo-catholics and evangelicals, Christian socialists and modernists can all "agree to disagree" while coming to the altar together to worship God. The act of worshipping together in grace knits them into a Christian community, not their uniformity of propositional belief. On the other hand, when Primate X refuses to worship with Primate Y, for instance, we have a failure of comprehensiveness--a failure which prima facie strikes at one of the constitutive features of Anglicanism.
But for its critics, comprehension is hardly a virtue; it is a confusion, perhaps, one infers, even serving to mask a steady liberalization of dogma. For instance, Al Kimel some time ago raised an argument from Eric Mascall purporting to show what is wrong with comprehensiveness:
[a] The fundamental incoherence of the three-school theory can be seen from the obvious fact that the existence of each one of the schools can be justified only on the assumption that its characteristic theological assertions are true. [b] But in that case the characteristic theological assertions of all the three schools must be mutually compatible. And in that case there is no reason why we should not accept them all and a great many reasons why we should. [c] But then what will have happened to the three schools? It is quite ridiculous to envisage the Church as a tricorporate society, each of whose parts is committed to holding one third of the truth. Regrettable as this no doubt is, it is because each school has not been convinced that everything that the others were holding was part of the truth that the schools have remained recognisably distinct.
I have added letters in brackets to mark key points in Mascall's reasoning; my use of boldface indicates important words. [a] contains an extremely strong claim; in effect, the parties of Anglicanism presume that their distinctive theology is simply true. That presumption is their reason for being. On [b], they could then only be comprehended in Anglicanism if their theologies were logically consistent. But, according to [c], their theologies are not logically consistent--each party envisions itself as complete and not in need of coexistence with the others. Thus, a religion "comprehending" them would be entertaining contradictions; ergo, Mascall writes of "the fundamental incoherence of the three-school theory." And, taking his cue from Mascall's reasoning, Kimel writes "[t]he ideology of Anglican comprehensiveness is simply an impressive way of hiding the internal contradictions of our denomination."
I am not persuaded by Mascall, however. The soft point in his argument seems to me to be in [a]. He presumes each party could only mean for its theology to be taken in such a way that they contradict each other. For example, the Anglo-catholics assert "Q is true" and the evangelicals assert "Q is not true;" they must make their assertions without qualification as simply being the case, according to Mascall.
If they instead asserted "So far as we know, Q is true" and "So far as we know, Q is not true" then there would be no contradiction. Such qualification in the parties of Anglicanism is a mark of epistemic humility. Mascall's incoherence-argument requires epistemic hubris, namely the unqualified assertion of the position of one's party. But, givem our conviction that comprehensiveness--unity in worship--really is worth striving to maintain, it follows we should view Mascall's argument as a reductio of the practice of epistemic hubris. he does not do what he supposes, arguing that comprehension cannot work, but only that it cannot work without epistemic humility.