[…] the learning of a second language is precisely the same process as the learning of a first, of one’s own “mother-tongue” […] even coming to substitute, if circumstances favor, the second language in our constant and ready use, and to become unfamiliar with and forget its predecessor.
- Whitney (1875), a pag.24-25

We realize better in the case of a second or “foreign,” than in that of a first or “native” language, that the process of acquisition is a never-ending one […].
- Whitney (1875), a pag.25