 From an historical perspective, logical positivism represents a linguistic version of the empiricist epistemology of David Hume (1711–76). It refines his crucial distinctions of “relations between ideas” and “matters of fact” by redefining them relative to a language \(\mathbf{L}\) as sentences that are analytic-in-\(\mathbf{L}\) and synthetic-in-\(\mathbf{L}\), respectively. His condition that significant ideas are those which can be traced back to impressions in experience that gave rise to them now became the claim that synthetic sentences have to be justified by derivability from finite classes of observation sentences. Hume applied this criterion to exclude the idea of necessary connections, which are not observable, from significant causal claims, which were thereby reduced to relations of regular association, spatial contiguity, and temporal succession. And logical positivism followed Hume’s lead.