What U.S. law am I talking about? ALL U.S. law concerning granting citizenship at birth - of course. This is not avoiding answering your question - it is answering it directly.
One need not have any citizen parents at the time of birth to be a U.S. citizen at birth - as is the case with Marco Rubio - whose parents were legal residents of these United States.
If there are currently only two types of U.S citizen, then a U.S. citizen at birth is a natural born citizen; and the other category must be naturalized via a legal process and sworn oaths of allegiance as outlined under Congressional power to adopt a uniform rule of naturalization.
Where do you find another category mentioned?
Did I claim there was another category mentioned?
What U.S. law am I talking about? ALL U.S. law concerning granting citizenship at birth - of course.
Well what law in particular is that? It must not be "the Constitution" else you would have said so. Isn't citizenship only "granted" under naturalization laws?
One need not have any citizen parents at the time of birth to be a U.S. citizen at birth...
I agree. They're naturalized under USC 8, the section of uniform rules of naturalization Congress was empowered to write, because the parents are aliens. Oh, the parents have to be here legally as well for that section of law to apply.
Is USC 8 the US law which you believe makes someone a natural born citizen?
If there are currently only two types of U.S citizen, then a U.S. citizen at birth is a natural born citizen...
How many citizen parents must that person being born have to qualify as a natural born citizen?
A direct answer would be appreciated as you've not directly answered it as of yet.
“One need not have any citizen parents at the time of birth to be a U.S. citizen at birth - as is the case with Marco Rubio - whose parents were legal residents of these United States.”
That is a false statement. Marco Rubio’s parents were foreign citizens and what are known as aliens in amity, and their son was born with natural born Cuban citizenship and statutory U.S. citizenship at birth. Statutory citizenship at birth is generally comparable to being an English subject made at birth, rather than a subject born. Under the English laws at the time of the adoption of the Constitution and earlier, an English subject made was a form of naturalization at birth by the man-made and therefore unnatural act of a statute from Parliament.