A pragmatic conception of logic, however, leads him to view its instrumental-methodological character as primary with respect to the doctrinal features. All this follows quite naturally from what we said above, because, for a pragmatically oriented thinker, logic's task lies, first of all, in systematizing and rationalizing the practice of reasoning in all the contexts (theoretical included) where human beings usually draw inferences. Logical rules, in turn, are not supposed to have an abstract and formalistic character, because in that case they cannot be attuned to human practices (be they theoretical or instrumental). It is interesting to note that this approach is not distant from some insights contained in the works of the second Wittgenstein, where language is no longer taken to be an ideal entity endowed with some sort of "essence," but rather a set of social practices that are used in order to satisfy men's concrete needs. Our models of inference thus become the products of social practices, while the social dimension pertains to language in each of its many characteristics and features. In other words, our rules for drawing inferences are essentially practical and not formal; they are rules that allow (or do not allow) us to perform a certain kind of action.

For Rescher a conceptual scheme for operation in the factual domain is always correlative with a Weltanschauung - a view of how things work in the world. And the issue of historical development becomes involved at this juncture, seeing that such a fact-committal scheme is clearly a product of temporal evolution. Our conceptions of things are a moving rather than a fixed target for analysis. The startling conclusion is that there are assertions in a conceptual scheme A that are simply not available in another conceptual scheme B, because no equivalent in it may be found. This view also allows him to challenge Donald Davidson when he says that, "we get a new out of an old scheme when the speakers of a language come to accept as true an important range of sentences they previously took to be false." The point at stake, in fact, is different, since Rescher answers that a change of scheme is not just a matter of saying things differently, but rather of saying altogether different things.

In other words, a scheme A may be committed to phenomena that another scheme B cannot even envisage: Galenic physicians, for instance, had absolutely nothing to say about bacteria and viruses because those entities lay totally beyond their conceptual dimension. Where one scheme is eloquent, Rescher says, the other is altogether silent. This means, moreover, that our classical and bivalent logic of the True and False is not much help in such a context. Some assertions that are deemed to be true in a certain scheme may have no value whatsoever in another scheme, so that we need to formalize this truth-indeterminacy by having recourse, say, to a many-valued logical system in which, besides the classical T and F, a third (Indeterminate) value I is present. We have, in sum, a more complex picture than Davidson's. Rescher observes that in brushing aside the idea of different conceptual schemes we incur the risk of an impoverishment in our problem-horizons. So, to deny that different conceptual schemes exist is absurd.