Certainties, truth and relativism
If we compare the picture that we can extract from On Certainty with Davidson’s view (as expounded in, e.g., ‘A Coherence Theory of Truth and Knowledge’), the important difference seems to be this, that Wittgenstein introduces the layer of certainties in between our epistemological practices and external reality, whereas Davidson construes the relation between belief and reality much more directly. The fact that certainties are categorically different from beliefs and other epistemological entities (despite the fact that over time, and between communities and/or individuals, what counts as what may change) in combination with the plurality of systems of certainties, makes room for a measure of (conceptual) relativism that Davidson seeks to avoid. His way of doing so is to take the core of our belief system to be as stable (over time, over communities and/or individuals) as is the causal influence of external reality on humans. (There is more room for differences in the ‘superstructure’ of complex beliefs that are not directly caused by our interactions with reality, but that is something that Davidson does not pay that much attention to).
This has also consequences for how truth works in both perspectives. In On Certainty truth is first and foremost a concept that operates within a particular epistemological practice, that itself is made possible by a particular system of reference consisting of certainties. (That Wittgenstein construes it in more or less verificationistic terms is an additional, independently motivated feature.) The relation between external reality and certainties is not one of determination, but of constraint. This is the source of plurality, and it also implies that certainties are not upheld because they are true. The fact that different certainties can be upheld at the same time also testifies to that, of course. Nevertheless, certainties differ in terms of their entrenchment and some are so basic to our form of life that it does not seem that much of a stretch to call them ‘true’, admittedly in quite a different sense. In Davidson’s perspective we also have two distinct properties. ‘Mild correspondence’ is the notion of truth that links beliefs (and hence meaning) to the world. It is what the causal influence of the world on us results in. Internally, i.e., within our actual epistemological practice, truth then takes on a different form, that of coherence.