 These cases illustrate that concepts can and do get extended to fresh new domains in which theories are uncertain and experience scant, even if no definite measurement operations have been worked out. We start with a concept with a secure net of uses giving it stable meaning in a restricted domain of circumstances. The extension of such a concept consists in giving it a secure net of uses, also credibly linked to the earlier net, in an adjacent domain. Such extension can happen in all kinds of ways, including theoretical fiat and metaphysical presumption, but the operational method is the most assured one. Specific, well-defined operations, whether they be instrumental, mental or paper-and-pencil type, can start a secure skeleton of meaning in the new domain. With all the elements of new meaning operationally well-defined, it also becomes possible to attempt linking them up with each other at each step along the way and check the whole meaning for coherence. (Compare such a deliberate process with the vague presumption that terms in a theoretical equation must have the same meaning in the entire mathematical range given to the variables.) Operationalism in this guise can be used as a secure method of conceptual extension, quite the opposite of the kind of fragmentation that Hempel feared. Such operationalism would not destroy systematic unity; on the contrary, it is an optimal strategy for achieving as much systematic unity as nature would allow, in a strongly empiricist system of knowledge.