[…] so long as every change which arises in the local parts A and B and C, and so on, works its way through all the rest […] so long will the language X remain one […] But separate […] the parts A and B and C from one another, so that the changes in each are made in that alone, and do not extend into the rest, and the peculiarities of each will begin to be confined to itself; what we call dialectic growth will set in; the process of divarication into diverse languages will have begun […].
- Whitney (1875), Pag. 164

The most instructive attainable example of dialectic growth […] is that presented us in the Romanic languages, because we have there a most important and widely-spread body of highly cultivated languages, each with its legion of subsidiary dialectic forms; and also […] the very mother, the Latin, from which they have all sprung.
- Whitney (1875), Pag. 166

This cutting off, by cessation of communication, of a common regulative influence over the never-ending changes of speech, may seem a very slight cause of divergence, and so in truth it is; but it is fully sufficient to account for all the phenomena of dialectic growth.
- Whitney (1875), Pag. 165