The Justificationist's Response to a Realist

Abstract

Justificationism differs from realism about how linguistic meaning is given, and hence in its associated conception of truth, and in particular in rejecting bivalence. Empirical discourse differs from mathematical primarily in that an effective decision-procedure for an empirical statement may cease to be available at a later time. The contrast is not that empirical knowledge is derived from what is mind-dependent, namely perception, whereas mathematical knowledge is not so derived. Mathematical knowledge does not accrue simply because a proof exists: the proof has to be understood and recognized to be valid. Most ordinary mathematical proofs are indirect: they supply an effective means, in principle, to construct a direct or canonical proof. An indirect justification for asserting an empirical statement does not, in general, supply a means for bringing into existence a direct justification; it merely provides a ground for supposing that a direct justification would be or have been available for someone suitably placed to make the necessary observations. But it is by what constitutes direct evidence for a statement that its meaning is given; a grasp of its meaning does not rest on an ability to survey all conceivable indirect evidence. A direct justification of an empirical statement of the kind capable of being used as a report of observation must be an actual or possible observation by a suitably placed observer. A possible observation need not be explained by means of a counterfactual: it may be taken as consisting of the appropriate physical stimuli. This way of understanding it evades all three of the untenable choices Peacocke offers the justificationist. Unlike mathematical ones, empirical statements are often justifiably asserted on probabilistic grounds. When the statement admits of a conclusive justification, probabilistic evidence will not figure as a direct justification for asserting it, and hence as determining its meaning, so no circularity is involved, as Peacocke charges. There may, however, be empirical statements that can neither be reports of observation nor admit of a conclusive justification. Such statements can be asserted only on inductive or abductive grounds; this goes to characterize their meanings. Their meanings must therefore be explained by specifying such grounds as the most direct justifications of them that can be given, although they are difeasible rather than conclusive. Peacocke appears to deny that there can be statements that transcend all possible verification. To vindicate such a view from a realist standpoint is surely very difficult: it requires a demonstration that we could not grasp what it would be for such a statement to be true. It is very obscure what a realist's conception of truth is. The principle of bivalence remains a strong mark of differentiation between a justificationist and a realist conception of truth; a clear argument why the principle should be accepted would greatly help to clarify how the realist conceives of truth. I enjoyed reading Peacocke's article, but remain as perplexed as I was before just how he does conceive of truth.