The meaning of natural born citizen can be deduced from other writings know well by the founders. Black's Law of Nations defines a natural born citizen is one who's parents (plural) are citizens and being born in the same country. It's meaning would be there is no other possibility of citizenship at birth. If either parent is has different citizenship or the place of birth is a different country then that new born can claim some form of citizenship of different countries. Also, in the original writing of the Constitution the founders grandfathered themselves to be President since none were natural born citizens of the USA.