Many scholars who engage in heavily theological interpretations of the Bible will, at some stage, come up with a tu quoque defence for defending their theological bias. The tu quoque defence begins by pointing out that all rational argumentation is ultimately ungrounded, and that all arguers have presuppositions which must be based on their (biased) preferences. This is true. But the apologetic use of the tu quoque defence involves the additional step of arguing that the theological bias is therefore as warranted as any other. This is more than highly questionable. By far the most developed exposé of the “But you’re biased, too!” defence of theological interpretation is by William Bartley, in The Retreat to Commitment (rev. edn. 1984).
Bartley describes the argument made by theologians, from the limits of rationality:
“This argument is that the most important ideas—presuppositions, first principles–cannot be justified or criticized, and are hence beyond rational evaluation; moreover, that all individuals must, for logical reasons, hold such ideas; and that, as a consequence, anyone has a sound excuse for being uncritically committed to some such first principle or dogma. This argument, itself an idea about rational argumentation, has the effect of protecting certain other ideas from rational argumentation by removing them from competition. In effect, the argument decrees that our most fundamental ideas are not and need not be in argumentative competition with other ideas (i.e., are beyond criticism) due to an intrinsic logical feature of argumentation.” (xx)
If the argument is accepted, the resulting problem is relativism:
“[The problem is] whether some form of relativism is inescapable because rationality is so limited, logically as well as practically, that the choice between ultimately competing religious, moral, and philosophical positions is, in the last resort, arbitrary. For example, is an individual’s decision to become a rationalist—even from a rationalist point of view—any less subjective, relative, arbitrary, rational than an individual’s decision to become a Christian?” (xxv)
And when used by Protestant apologists, such as Karl Barth, it becomes a defence of fideism:
“By resorting to the argument about the limits of justification and criticism and of rationality, Protestantism in a sense gives up the battle; it removes its basic principles from the competitive arena, and engages in a sort of intellectual counterpart of economic protectionism. This is sufficient, as we shall see, to render it an ideology.” (xxii)
“wherever used, it [this argument] provides the custodians of ideas with a rational excuse that permits them to protect their own principles from competition—whether these be claimed to be the principles of science (for there are also many ideologists of science), or political principles, or whatever. This argument transforms whatever it touches into pseudo-science and ideology.” (xxii-xxiii)
“the Christian commitment of many Protestants depends upon the assumption that it [the problem of the limits of rationality] cannot be solved. For the argument provides a rational excuse for irrational commitment.” (72)
“The theologian makes an irrational commitment to Christ; he admits it—he glories in it. But the rationalist has made an equally irrational commitment to reason—despite his insolent claim to “hold no dogma sacrosanct”. The theologian, it appears, is intellectually more honest-indeed, even more rational-than the rationalist.” (77)
Bartley concludes that the retreat to commitment is the only serious apologetic argument able to be made for Christian theology today:
“The only serious argument for Christian commitment today concerns the problem of the limits of rationality. This is the argument that both Kierkegaard and Barth relied upon.” (72)
Bartley’s own solution is essentially Popperian. Bartley gives up the attempt to positively justify one’s position, on the recognition that the most one can do is to provide falsification of positions. That is, full positive justification of a particular interpretation is always out of reach. However, it is quite likely that some interpretations will turn out to be better than others in the light of critical discussion and tests. At the very least, it is possible to evaluate and rank interpretations according to their success in explaining all the evidence.
Bartley’s answer gives a good reply to those apologists who rely on the ultimate groundlessness of knowledge, so as to defend their fideism. I’m not so sure that it deals with the subjectivity involved in selecting and evaluating data, but the critical process to which this is subjected means that the relativistic argument is itself relativised. All up, Bartley provides a fine and detailed examination of the apologetic move of Barth and others, in which they appeal to the relativity of knowledge in order to make an argument–not for relativism, but–for fideism.