In historical linguistics, the uniformitarian principle is the assumption that processes of language change that can be observed today also operated in the past.
In linguistics, Uriel Weinreich, William Labov and Marvin Herzog appear to have been the first to expressly elaborate, in the 1960s, on a hitherto tacit assumption of equivalent processes being at play in the present time as in the past.
Hermann Paul, for instance, assumed what he the called "psychological" principles in the 1860s as underlying language change.
[3] Around the same time William Dwight Whitney wrote of "So far back as we can trace the history of language, the forces which have been efficient in producing its changes ... have been the same".
[4] Labov summarizes the state-of-the-art: "Today, it would seem that linguistics has accepted the uniformitarian principle and its consequences, as geology, biology, and other historical sciences have done.