There is […] an element of constraint in language-learning. But it is an element of which the learner is wholly unconscious. Whatever language he first acquires, this is to him the natural and necessary way of thinking and speaking; he conceives of no other as even possible.
- Whitney (1875), a pag.22

When we first take hold of an additional language, we cannot help translating its sign into those we already know; the peculiarities of its “inner form,” the non-identity and incommensurability of its shaped and grouped ideas with those of our native speech, escape our notice. As we gain familiarity with it, as our conceptions adapt themselves to its framework and operate directly through it, we come to see that our thoughts are cast by it into new shapes, that its phraseology is its own and inconvertible. Perhaps it is here that we get our most distinct hint of the element of constraint in language-learning.
- Whitney (1875), a pag.23-24