When did surnames become a "thing" (i.e. a hereditary legal requirement)?

by urbananchoress

I was venting to my sister about a difficult day I'd had at the library because like 90% of the men mentioned in a particular bishop's register were called John and it was hard for me to keep track of them. She asked why I didn't just refer to them by surname - but that's not always possible with medieval surnames. Many people didn't even claim to have a surname (e.g. 'John, of the village of Hampstead ...). As far as forming one went, I guess you could technically have

  • father's name (John Wayne)
  • patronym (John Watson)
  • occupation (John Smith)
  • place of birth, especially for monastics.

What I want to know is: when did surnames become 'fixed' and hereditary? When would John Smith's son Thomas remain Thomas Smith and not call himself Thomas Baker or Thomas Butcher?

hillsonghoods

There's always more to say in answer to this, but /u/yodatsracist's answer to the question When and why did surnames begin to be used? might be a place to start.