Not quite true that nobles and priests were the only ones that knew how to read. Lower classes absolutely knew how to read they just didn’t use that knowledge for writing books - they used it for communicating and for legal purposes. The lower classes were actually quite litigious and a subsect of them required literacy as a means of self advocacy, occasional resistance and survival.
The concept of the peasantry being unschooled, idiot commons without the brains and means to aquire knowledge has always been a way to keep you and I, people who came after as their legacy, distanced from their history so we could instead align ourselves with the rich and powerful who could be seen as the “creators” of society and culture.
Those peasants and serfs were a lot more like us than people think.











There is evidence of a number of uses of vernacular written language in archeological sites. The matter of literacy as mentioned around the advent of the Doomsday Book was not a measure of who could read common vernacular they way literate tends to mean today. It was a measure of who had completed their letters. A set form of schooling that covered about six years worth of language education and numeracy. So it’s kind of hard to track actual literacy rates given sources at the time because the bar to count as “literate” by census records was specific. The majority of college level modern users of language would be unable to clear that bar. I would not be considered literate because I can only write vernacular. So you are semi-correct in that sense yes only nobles and men of the church were “literate” by standards of the time.
There are a number of archeological finds throughout the medieval ages that showed a general upward trend of the skill of being able to read and write fairly basic missives amongst humble people. A lot of our surviving evidence of peasant writing is on very rudimentary materials like bark and it is very practical use. People learned the skill from other people for doing stuff like writing IOUs or orders for goods or as reminders and most examples that survived were under 20 words in length. In a lot of places being able to read and write wasn’t considered remarkable enough to record as a special skill unless you could do it in Latin. This is why you find books written for common people like the Dite de Hosebondrie ( Husbandry) for the peasant farmer or guides for common housewives in the 13th century in “rustic” language styles. Books were uncommon and expensive and you had to go to them to read them but the people who they were written for weren’t always nobles or clergy.
https://www.medievalists.net/2024/11/medieval-daily-life-on-birchbark/