In some countries, surnames weren’t established until the 17th century or later. In England, under king Henry VIII, children from marriages were to bear the surname of the father, and women had long changed their last name to that of their husband upon marriage.
Family names for nobility had long been established to indicate which place was attached to their house (territorial name). In France, this was the custom as well, using ‘de’ to indicate which land the family owned.
In French-speaking Canada and in France during the 1600s and later, the church began to require the recording of all the parish highlights: baptisms, marriages, and burials. Legal documents were kept in town registries by royal notaries: court cases, law suits, sales of property, and so forth. Married women were recorded in parish or legal documents using their maiden surnames, along with the full name of their husband, even if widowed. Marriages and baptisms included the names of their parents and often where they were from. All of this record-taking makes it much easier today to know who the parents of both our male and female ancestors were.
There was a time when a given name (first name) sufficed to identify people, but when the Middle Ages arrived, a mix of population and demographic growth made it imperative to choose a surname (last name).
At the end of the fourteenth century, France already had between ten to twenty million inhabitants. Surnames, which were to be inherited family names, had diverse origins: geographic features such as mountains (La Montagne) and rivers (La Rivière), and places (De Berry), professions or trades (Marchand, Prévost, Mercier) and personality or physical features (Le Sage, Le Tendre LeBlond).
One must realize that when last names began to be established to connote family groups, not everyone had the privilege of a formal education and so could not read or write. There were also no standard rules of grammar for the French language. When someone who was illiterate needed to add their name to a document, they would provide it phonetically and then it was up to the notary or cleric to spell it the way they believed it should be spelled.
It is therefore not unusual that the spelling for a name might change over time. For example, we see the last name Roy spelled multiple ways in multiple documents: Le Roy, le Roy, Leroy, Le Roi, and so forth. Today the name is mainly without the article: simply ‘Roy.’