English and Welsh

"English and Welsh" is J. R. R. Tolkien's inaugural O'Donnell Memorial Lecture of October 21, 1955. The lecture sheds light on Tolkien's conceptions of the connections of race, ethnicity, and language.
Publication.
It was first published in "Angles and Britons" in 1963, and then was later republished in "The Monsters and the Critics, and Other Essays".
Contents.
Tolkien begins with an overview of the terms "British", "Celtic", "Germanic", "Saxon", "English" and "Welsh", explaining the last term's etymology in "walha".
Tolkien also addresses the historical language contact between English and Welsh since the Anglo-Saxon invasion of Britain, including Welsh loanwords and substrate influence found in English, and conversely English loanwords in Welsh. Comparing the Germanic "i"-mutation and the Celtic affection, Tolkien says:
In the final part of the lecture, Tolkien explores the concept of phonaesthetics, citing the phrase "cellar door" as a recognized beautiful-sounding phrase in English, 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:
Tolkien alludes to his view that such tastes are inherited, "an aspect in linguistic terms of our individual natures. And since these are largely historical products, the predilections must be so too." To refer to such an inherited taste of language, Tolkien introduces the term "native tongue" as opposed to "cradle tongue".
Influence.
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. More beautiful than, say, 'sky', and far more beautiful than 'beautiful' … Well then, in Welsh, for me cellar doors are extraordinarily frequent". This heavy interest in and appreciation of Welsh influenced his own languages, notably his elvish languages like Sindarin and Quenya.
This lecture is considered Tolkien's "last major learned work". There were several important aspects to it: firstly, it "includes a valuable contribution to the study of the place of Britons in Anglo-Saxon England", secondly, a warning against racial theories, thirdly, a hypothesis of "inborn" linguistic tastes which then leads into a discussion of his own views of aesthetics in language, and finally, it provided a (correct) hypothesis on the origins of the word "w(e)alh", which in turn provided an explanation of what happened to Celtic when the Anglo-Saxons invaded.