[…] it must be distinctly laid down as a fundamental principle in linguistics, that no fact in human expression is fully estimated, until it is seen in the light of related facts all through the domain of universal expression.
- Whitney (1875), Pag. 191

As linguistics is a historical science, so its evidences are historical, and its methods of proof of the same character. There is no absolute demonstration about it, there is only probability, in the same varying degree as elsewhere in historical inquiry. There are no rules the strict application of which will lead to infallible results.
- Whitney (1875), Pag. 312