Comparing the Germanic i-mutation and the Celtic affection, Tolkien says: The north-west of Europe, in spite of its underlying differences of linguistic heritage – Goidelic, Brittonic, Gallic; its varieties of Germanic; and the powerful intrusion of spoken Latin – is as it were a single philological province, a region so interconnected in race, culture, history, and linguistic fusions that its departmental philologies cannot flourish in isolation.In the final part of the lecture Tolkien explores the concept of phonaesthetics, citing "cellar door" as a phrase recognised as sounding beautiful in English and adding that, to his own taste, in Welsh "cellar doors are extraordinarily frequent".
Tolkien describes the working of phonaesthetics inherent in the moment of association of sound and meaning: [T]his pleasure is felt most immediately and acutely in the moment of association: that is in the reception (or imagination) of a word-form which is felt to have a certain style, and the attribution to it of a meaning which is not received through it.Tolkien alludes to his view that such tastes are inherited, "an aspect in linguistic terms of our individual natures.
Tolkien notes in his lecture that "Most English-speaking people … will admit that 'cellar door' is beautiful, especially if dissociated from its sense and from its spelling.
Third, it presents Tolkien's hypothesis of "inborn" linguistic tastes, which then leads into a discussion of his own views of aesthetics in language.
Finally, it provides a (correct) hypothesis on the origins of the word "w(e)alh", which in turn provides an explanation of what happened to Celtic when the Anglo-Saxons invaded.