The present paper purports partly to reexamine and partly to summarize several points which occupied and still occupy a central position in more recent discussions among empiricist philosophers. As such discussions are essentially attempts at the clarification of terms, it might also be said that this essay intends to contribute to the analysis of certain very general and highly ambiguous expressions. The words in question are, first and mainly, ‘hypothetical’ and, more incidentally or by the way of exposition, ‘atomic', ‘elementaristic', and ‘extensional.’ In general, it is an attempt to show the impact of some of the ideas developed in the work of Carnap; within a prevailingly logical frame of reference in The Logical Syntax of Language and, in a more epistemological setting, in Testability and Meaning. In particular, it wants to eliminate some ambiguities which could arise from an oversimplified reading of certain passages in TM, as for instance: “If by verification is meant definitive and final establishment of truth, then no (synthetic) sentence is ever verifiable” (p. 420). If this passage is understood to assert that every synthetic sentence is hypothetical, then it is either false or several meanings of ‘hypothetical’ are to be distinguished. This distinction, implicit in TM, will upon closer examination prove to be related to the fundamental distinction between statements within and statements about a linguistic structure.