This results from the fact that, up to five or six, children in town, brought up in a room and under the care… — Jean Jacques Rousseau

This results from the fact that, up to five or six, children in town, brought up in a room and under the care of a nursery governess, do not need to speak above a whisper to make themselves heard. As soon as their lips move people take pains to make out what they mean; they are taught words which they repeat inaccurately, and by paying great attention to them the people who are always with them rather guess what they meant to say than what they said. It is quite a different matter in the country. A peasant woman is not always with her child; he is obliged to learn to say very clearly and loudly what he wants, if he is to make himself understood. Children scattered about the fields at a distance from their fathers, mothers and other children, gain practice in making themselves heard at a distance, and in adapting the loudness of the voice to the distance which separates them from those to whom they want to speak. This is the real way to learn pronunciation, not by stammering out a few vowels into the ear of an attentive governess. So when you question a peasant child, he may be too shy to answer, but what he says he says distinctly, while the nurse must serve as interpreter for the town child; without her one can understand nothing of what he is muttering between his teeth.

I grant you uneducated people and villagers often fall into the opposite extreme. They almost always speak too loud; their pronunciation is too exact, and leads to rough and coarse articulation; their accent is too pronounced, they choose their expressions badly, etc. But, to begin with, this extreme strikes me as much less dangerous than the other, for the first law of speech is to make oneself understood, and the chief fault is to fail to be understood. To pride ourselves on having no accent is to pride ourselves on ridding our phrases of strength and elegance. Emphasis is the soul of speech, it gives it its feeling and truth. Emphasis deceives less than words; perhaps that is why well-educated people are so afraid of it. From the custom of saying everything in the same tone has arisen that of poking fun at people without their knowing it.

Source: Wikiquote · CC BY-SA 4.0