My great grandfather changed his name from John Thomas Moriarty to John Taylor Lozon. He lived 1895-?1944. Would he have had to do this legally or could he simply just start using this new name. I understand why and when he started using the new name. I just would like to know the legality of doing this in the time he was alive. All census and legal documents use his changed name not his given name. Would he have to prove his identity? He never used a social security number but did they not use birth certificates?