I've talked about name changes - those frustrating ancestors who changed their names, causing great confusion for descendants. I've talked about Dutch patronymics and diminuitives and how to understand those names if you have 17th Century ancestors in New York.
But how do we know if all the variant names (patronymics, diminuitives etc) we find for an individual are truly for one person?? For example, how do I know that the man I find recorded in various 17th Century records as Cornelis Antonissen, Cornelis van Breuckelen, Broer Cornelis, Cornelis Teunis, and Cornelis Van Slyke is One individual and not several different men? For that matter, how do I know that there are not more than one man named Cornelis Antonissen running around in the same location in the same time period?
As the French say "Cherchez la femme!" (Look for the woman)
Most men who came to New Netherland (present day New York) married. Yes, some remained single but the majority married and had large families. When a spouse died, he or she was quickly replaced (an economic necessity) and families merged.
This means that one of the ways you can determine if Cornelis Antonissen and Cornelis van Breuckelen and Cornelis Van Slyke are the same person is to look for records which also name his wife (or children)
Another way to determine who an individual is, is to search court and land documents. These exist in great quantities for 17th Century New York and are available as published books. So, for example, if you find two men named Jan Albertsen, and are trying to determine if they are one and the same, find out if they lived in two locations at the same time.
Look for church records, especially baptisms. Who sponsored the children of the two Jan Albertsen individuals? Were the sponsors from entirely different families? Usually sponsors were family members or close friends. If you find that sponsors seem divided with one Jan Albertsen using sponsors from one distinct group and the second Jan Albertsen using sponsors from a second group, you probably are looking at two different men.
Check the naming patterns of his children. Usually children were named after each set of grandparents. If you know the man's father (which you determine from his patronymic) and his mother, as well as the wife's parents, you may be able to see a pattern of names that does not fit (because in fact it is two different families and not one). Conversely the naming pattern may fall nicely into place, indicating that you are probably looking at one individual and not two.
By the way, Jan Albertsen is a true example, and is one of the settlers I plan to write a book on for my New Netherland Settlers series. It's the story of two men with the same name who have been confused by genealogists for many years and erroneously merged as one man. The main secret to determing which man was which was to look at his wives, his children (their naming patterns) and baptismal sponsors.
Don't despair, take your time, check your facts carefully and you should be able to prove that your ancestor did indeed use 7 different names during his lifetime.