One problem with this sort of view, Geach points out, is that we could never have grounds for believing it. For there are really only two possible sources for a theological doctrine, either reason or revelation. To be more precise, one way we might come to know it is via philosophical argumentation whose premises are completely independent of revelation. Philosophical arguments for God’s existence would be an example. The other way is through special divine revelation, such as a message given through a prophet whose authority is backed by miracles. The doctrine of the Incarnation would be an example. Christianity traditionally appeals to both sources of knowledge, but what is distinctively Christian comes through revelation.
Now, the problem for the modernist identified by Geach is this. Modernism is a specifically Christian view. The modernist claims (falsely, to be sure, but still he claims) to preserve what is essential to Christian teaching. And what is essential to this teaching, Christianity says, was divinely revealed at the time of Christ and the apostles. Hence modernism cannot appeal to a purely philosophical argument to justify itself. It has to make some appeal to the content of this divine revelation given at the time of the Church’s origin.
But how do we know that something really is part of the content of this revelation? Geach points out that continuity of teaching is a necessary condition of our knowing it. To be sure, it is not a sufficient condition. If some doctrine has consistently been taught by the Church for two millennia, that does not by itself guarantee that it is true, since we need some independent reason to think it really was divinely revealed two millennia ago. But, again, it is a necessary condition. If some doctrine has not been taught for two millennia, or even conflicts with what has been taught for two millennia, it can hardly be known to have been part of the divine revelation that was given two millennia ago. And in that case it cannot be justified by appeal to that revelation.
The problem for the modernist is that the new doctrines he wants to teach, or the new interpretations he wants to give old doctrines, by definition cannot be traced to that original revelation from two millennia ago. If they could be, they would not be new. Hence the modernist cannot defend them by appealing to revelation any more than he can defend them by appealing to philosophical arguments. And since those are the only possible ways he could have defended them, he cannot defend them at all. They simply float in midair, ungrounded. Thus does Geach say of the modernist:
His teaching will be a matter of learned conjectures intermixed with such fragments, few or many, of the old tradition as he chooses still to believe. He may choose to believe all this; but he will scarcely persuade a rational outsider, and he can claim no authority that should bind the conscience of a Christian. (p. 86)
Modernism is in this way an inevitably self-defeating position. By rejecting the continuous teaching of tradition, it rejects the only basis for its own teaching that it might have had.
In my early years as a grad student I took a class with John Hick (who was one of the best teachers I ever had, even if his philosophical and theological views left much to be desired). Hick was a modernist if ever there was one, and an influential proponent of the religious pluralist view that all of the world religions are more or less equally good and salvific. Now, you can’t coherently take such a view unless you drastically water down the truth claims of these religions, since those claims conflict with one another. And Hick acknowledged (in conversation – I don’t know offhand if he ever said this in print) that few people were likely to convert to Christianity or any other religion in such watered-down forms. There simply isn’t much point in converting to Christianity if you’re told from the get-go that doctrines like the Trinity and the Incarnation are not really true, but just poetic ways of speaking. Hence, for views like his to prevail, Hick acknowledged, people have to start by believing the more traditional doctrines and then gradually move away from them under the influence of arguments like his.
This illustrates how modernism is psychologically and sociologically parasitic on the traditional doctrines it rejects. But Geach’s point is essentially that modernism is also logically parasitic on the doctrines it rejects. For it has no freestanding basis, but presupposes the traditional view that there really was a divine revelation two millennia ago, of which (modernism claims) it is itself at long last the correct interpretation.
Yet at the same time, and in the manner we’ve seen, modernism subverts any confidence we could have in a claim to know such a revelation. If you say “Such-and-such really was revealed two millennia ago, but the Church has misunderstood it for two millennia,” that inevitably raises the question “If you’ve been getting the content of the revelation wrong for that long, why suppose you’re right even about there having been any revelation in the first place?” Hence it is no surprise that it is only ever theologically conservative brands of Christianity that thrive, while liberal denominations shrink and die out. Logically, and thus psychologically and sociologically, modernism inevitably destroys the faith it claims to be preserving by adapting it to modern times. Modernism is in this way like a cancer that slowly kills the host on whose life it depends.
There is another irony in modernism, and one to which Geach also calls our attention. He writes:
It is often said that in our world and time the Christian story is irrelevant. A curious adjective, when the grimmest Christian prophecies of the last days might seem, even by human calculation, all too likely to be literally fulfilled. (p. 84)
If the prophecies in question seemed close to fulfilment in the 1970s, when Geach was writing, how much more so in light of the unprecedented moral depravity and runaway heterodoxy of the present day? Be that as it may, though modernism claims to save Christianity from being “irrelevant,” it is in reality an instance of the widespread apostasy from the Catholic faith that is among the things grimly prophesied by Christ and the apostles. In that way, the prevalence of modernism inadvertently confirms the predictions of the traditional theology it aims to subvert.