This peculiarity is probably one of the major stumbling blocks in French-Canadian genealogical research. Since last names (surnames) came into being for the purpose of identification, you could say that the "dit" name (pronounced "zeet") came into being for the purpose of further identification of a person or family.
Translated into English, "dit" (masculine) or "dite" (feminine) means "called" or "also known as." There is no negative connotation implied as is sometimes the case with the English "alias." The reasons or explanations for the name changes are infinite ... at least as infinite as there are actual individual changes. However, there are some general sources for these changes or identifications. Some of them are:
- Physical or character description
- Easily pronounced names
- Occupation or guild
- Seigneurial identification
- Place of origin
- Maternal identification
- Heroic deed or accomplishment
- Description of some object
The two surnames can be interchanged at any time ... "dit" is sometimes replaced by a hyphen. For example, Morin dit Valcourt may appear as Morin-Valcourt. And, since one or both forms of the name may appear at birth, baptism, marriage, in a census record or at death, each individual document must be checked to determine its use. A man might have been born as Jean-Baptiste Morin dit Valcourt, baptised as Jean-Baptiste Morin, married as Jean-Baptiste Valcourt dit Morin, found in a census as Jean-Baptiste Valcourt and died as Jean-Baptiste Morin Dit Valcourt!
The marriage repertoires that I've used used as primary guides for marriage data have therefore been read with care, for they usually gave me some clue as to a possible name change or double-identification.