For many centuries Norwegians had only one name -- their Christian, or first name, given the child when it was christened. The second name was the patronymic form -- that is, if a man's first name was Hans, his daughter was (firstname) Hansdatter and his son was (firstname) Hansson. In the 1870's legislation was passed which stated that women should use the masculine form for their patronymic. Therefore, Guri Johnsdatter became Guri Johnson.
Those who lived in rural areas also used a third name to indicate where they lived -- the farm name. When people moved from one farm to another, their last name became the name of the new farm. It wasn't until after 1900 that legislation mandated that people must take permanent family names. Some took the name of the farm while others took the patronymic. www.rootsweb.ancestry.com
This explains so much! I have been attempting to unscramble my family history for years now and have always been confused about what I thought were the weird names that I keep coming across. Now I have a place to start and can track down some of this information. I guess I now have a project for the week! I will now be able to link back to the fathers of these women that I am related to.