A natural born citizen is a person with U.S. Citizenship who does not have to state an oath of allegiance or be issued a certificate to establish citizenship.I am a natural born Citizen, but my government rightly required that I prove this via various official certifications in order that I be issued a passport, but I never was required to go through a naturalization process, which I think is your intended point, i.e., natural born Citizens don't need to be naturalized.
The question we must ask ourselves is, while this certainly is a necessary condition to being a natural born Citizen, is it a sufficient condition?
I think the founders answered that question in the Constitution and in their use of the very phrase itself, natural born Citizen. Washington and several presidents following were not natural born Citizens, which is why they added the "grandfather clause" to the eligibility requirement. Yet, were these founders required to formally state an oath of allegiance or were they issued a certificate necessary to establish their citizenship? As far as I know, they were not. (Do you know otherwise?)
As you know, regarding presidential eligibility, the Constitution does not state that one must simply be a "born citizen," but specifically states that one must be a natural born Citizen. We also know that the founders labored, deliberated and debated over the content of the Constitution for many months.
When it came time to put quill to parchment they most certainly did not add superfluous, meaningless words. If they had meant to allow the broader category of "born citizen" they would have succinctly stated such and not bothered to include the further restrictive qualification of being a natural born Citizen, which clearly excludes many types of mere "born citizens."
Note that the original founders were our new country's first natural citizens, yet they did not consider themselves to be natural born Citizens. This informs us, as is obvious from the very phrase itself, that natural born Citizen is an exclusive condition consisting of only the overlapping parts of its requirements.
Now, ask yourself, who are by far the most common, everyday ordinary type of citizens that naturally populate and perpetuate our great country, the type of citizens who, by their very nature, can only be U.S. citizens and nothing else? The answer is obvious - those born exclusively in country jurisdiction to existing U.S. citizens. These are the only type of citizens who are born with 100 percent, red-blooded exclusive allegiance to no other country but America. These are the natural born Citizens.
“Yet, were these founders required to formally state an oath of allegiance or were they issued a certificate necessary to establish their citizenship?”
Yes, I believe they were required to state an oath of allegience to become a citizen of their state. George Washington’s mother, Mary Washington, remained loyal to the Crown even after her son led the revolution against the Crown.
Mary Washington was allowed to keep her land holdings in Virginia after the British were defeated, even though she remained a Loyalist until her death. Later, when the Constitution was ratified, only citizens of the states consisting of the United States became citizens of the United States. To my knowledge, Mary Washington never became a citizen of the United States. Yet, she remained in the United States until her death and passed on vast land holdings to her heirs.