On the contrary, that duality is already forcing itself upon the economic sciences. Here, in contrast to the other sciences, political economy and economic history constitute two clearly separated disciplines within a single science; the works that have recently appeared on these subjects point up the distinction. Proceeding as they have, economists are-without being well aware of it- obeying an inner necessity. A similar necessity obliges us to divide linguistics into two parts, each with its own principle. Here as in political economy we are confronted with the notion of value; both sciences are concerned with a system for equating things of different orders-labor and wages in one and a signified and signifier in the other.
Certainly all sciences would profit by indicating more precisely the co-ordinates along which their subject matter is aligned. Every psychological relations that bind together coexisting terms and form a system in the collective mind of speakers.
Diachronic linguistics, on the contrary, will study relations that bind together successive terms not perceived by the collective mind but substituted for each other without forming a system.