The Notebooks of Schubert Ogden

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On Transcendental Deduction as Mode of Argument


From the general principle that one can infer from the reality of x to the reality of whatever is, in fact, a necessary condition of the possibility of x, it by no means follows, without more ado, that one can infer to the reality of y from the reality of x. For that to follow, there must be argument to the effect that y, in reality, is a necessary condition of the possibility of x—so that: ∼y ⊃∼x. 

But, further, even if this premise is argued for, it is important to be on the lookout for the fallacy of four terms that is likely to occur when the meaning of y in ∼y ⊃∼x is different, however subtly, from the meaning of y in x ⊃y. Put differently: in a valid reductive argument, the only condition whose necessity can be asserted in the conclusion is the same condition that is asserted in the major premise and therefore also requires to be argued for. 

That there are all sorts of arguments that are invalid either because they do not warrant their major premise or else commit the fallacy of equivocation in inferring from it to the conclusion seems clear enough. But consider, specifically, the following:

Rahner distinguishes, reasonably enough, between (1) "a historical certainty," such as exegesis must be content with establishing; and (2) "an existential certainty," such as belongs to faith and therefore must also be claimed by dogmatics and fundamental theology (Schriften zur Theologie, 9: 201 ff.). But when he tries to conclude, on the basis of this distinction, from faith's existential certainty that there is no place to go where there is more "clarity as to the meaning of existence" than in Jesus (Jn 6: 68 f.) to what he calls "the self­-understanding of the pre-Easter Jesus" (203, 201), his inference fails to convince because the connection that must exist between these terms is not established—either because "the self-understanding of the pre-Easter Jesus" is subtly ambiguous or because it is by no means evident that "clarity as to the meaning of existence" presupposes such a self-understanding in the sense in which he wishes to infer that it does. Thus, so far as it is valid, Rahner's argument establishes rather less than he claims, or seems to claim; while what he claims to establish is, as a matter of fact, not so much a conclusion of his argument as one of its tacitly assumed presuppositions. In somewhat the same way, one has every reason to ask whether, or to what extent, Rahner's valid reductive argument to the reality of Jesus' resurrection establishes the resurrection it purports to establish (219 ff., espec. 226). Here, to be sure, Rahner's own understanding of what we do and do not know about the "eschata" (221) approximates sufficiently closely to a minimalist understanding that the inference, in the sense in which he himself understands it, may be valid enough. But, then, it would be interesting to know whether the same could be said for the inference in the sense in which he allows most of his Catholic readers to understand it (because of his failure to make the necessary negations!). 

1971; rev. 5 August 2002

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