This is a legal memorandum about a subject in the headlines—whether Senator Ted Cruz is eligible to be president. My wife Karolyne goaded me for the opinion last Sunday, and I wrote it over the course of the day. It’s exactly what I would have written if I’d been retained by a client to research the matter. I’m a law professor, but I’ve also been editor in chief of Black’s Law Dictionary since 1994, roles that have left me with an unusual collection of books. Some are exceedingly difficult to track down—which is probably why nobody else writing about the issue seems to have cited them.
I’m a libertarian Republican—but I'm pretty apolitical. I’ve backed no presidential candidate in the current race. I’ve met Cruz only twice, but we haven’t seen each other or spoken in over two years. He didn’t ask for this opinion, nor have I communicated with him about it.
1. Foreign-born citizens as “natural-born citizens.” Article II, section 1, of the U.S. Constitution provides: “No Person except a natural born Citizen ... shall be eligible to the Office of President.” Does the phrase natural-born citizen include a citizen born outside the United States to one American parent? How did the Founders understand natural-born citizen?
2. Patriarchal vs. matriarchal lines. Does it matter whether the foreign-born American’s parent having U.S. citizenship was the father or the mother?
The conventional thought is that there are three paths to citizenship: (1) birth within a territory (traditionally known as jus soli); (2) naturalization; and (3) blood rights: the status of being the child of a citizen, even if born outside the territory (traditionally known as jus sanguinis).2 The U.S. Constitution appears to contemplate only the first two categories—not the third, which was created in 1790 by federal statute, one year after the Constitution was ratified.
Before its appearance in the U.S. Constitution, the phrase natural-born citizen was virtually unknown in Anglo-American law. It was analogized from the well-known phrase in English law, natural-born subject (subject being a citizen of a country governed by a monarchy). The two phrases are essentially identical.3 William Blackstone, the most widely read and influential writer on English law when the U.S. Constitution was drafted, had this to say:
The first and most obvious division of the people is into aliens and natural-born subjects. Natural-born subjects are such as are born within the dominions of the crown of England, that is, within the ligeance, or as it is generally called, the allegiance of the king; and aliens, such as are born out of it. Allegiance is the tie, or ligament, which binds the subject to the king, in return for that protection which the king affords the subject. The thing itself, or substantial part of it, is founded in reason and the nature of government; the name and the form are derived to us from our Gothic ancestors.4
Under English statutes, natural-born was extended in meaning over time to cover those born extraterritorially. Originally, only the children of a king’s ambassadors and other diplomats were held to be natural-born subjects, “for as the father, though in a foreign country, owes not even a local allegiance to the prince to whom he is sent; so, with regard to the son also, he was held ... to be born under the king of England’s allegiance, represented by his father, the embassador.”5 In 1352, to encourage foreign commerce, Parliament provided that all children born abroad would be natural-born subjects “provided both their parents were at the time of the birth in allegiance to the king”6—hence both parents had to be English subjects. In 1708 and 1731, the rules were liberalized “so that all children, born out of the king’s ligeance, whose fathers were natural-born subjects, are now natural-born subjects themselves, to all intents and purposes, without any exception.”7
The early federal statute noted above changed the common-law rule for the United States. In 1790, the First Congress enacted a statute establishing blood rights for foreign-born children of U.S. citizens and referring to them expressly as “natural-born citizens.”8 Here’s what it said: “[T]he children of citizens of the United States, that may be born beyond sea, or out of the limits of the United States, shall be considered as natural born citizens: Provided, That the right of citizenship shall not descend to persons whose fathers have never been resident in the United States.”9 The title of the statute was “An Act to establish an uniform Rule of Naturalization.”10 It was repealed shortly afterward. Five years later, a federal statute was enacted to the same effect, but it omitted the phrase natural-born citizen: “[T]he children of citizens of the United States, born out of the limits and jurisdiction of the United States, shall be considered as citizens of the United States: Provided, That the right of citizenship shall not descend to persons, whose fathers have never been resident in the United States.”11
The statutory basis for the rule has ebbed and flowed through the years. In 1802, Congress enacted a statute to providing that “the children of persons who now are, or have been citizens of the United States, shall, though born out of the limits and jurisdiction of the United States, be considered as citizens of the United States.”12 In 1855, Congress changed the benefit from “children of persons” to “children of fathers”: “All children heretofore born or hereafter born out of the limits and jurisdiction of the United States, whose fathers were or may be at the time of their birth citizens thereof, are declared to be citizens of the United States.”13 Not until 1934 did Congress relinquish the patriarchal preference that disallowed mother-citizens from conferring blood rights—making clear that this was a reversal of prior law.14 As late as 1961, the U.S. Supreme Court upheld this differential treatment by denying citizenship to the son of a father-alien (the mother was a citizen).15
Nineteenth-century American authorities tended to overlook blood rights and instead to focus on the first two categories: either birth within the territory or naturalization. The Fourteenth Amendment, which took effect in 1868, states: “All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States.”16 There the dichotomy is between born in the United States and naturalized. This Birthright Citizenship Clause clarifies that anyone born on U.S. soil is a citizen. It doesn’t affect the immigration statute that extended citizenship to the child of a nonresident citizen. Indeed, the U.S. Supreme Court has said that blood-rights citizenship is “not covered by the Fourteenth Amendment.”17
If that’s true, and if Article II covers the same types of citizenship as the Fourteenth Amendment, then there’s a gap in the Constitution: blood-rights citizenship isn’t covered. The question is whether natural-born citizen (Article II) is the same as person born in the United States (Amend. 14).
Even before that post–Civil War constitutional amendment, it was common to attribute the same meaning to natural-born as Blackstone did. In 1828, James Kent wrote his Commentaries on American Law, in which he equated natural-born citizen with native citizen. He closely paraphrased the applicable constitutional words from Article II and then gave the rationale for the provision. Note his use of native citizen: “As the President is required to be a native citizen of the United States, ambitious foreigners cannot intrigue for the office, and the qualification of birth cuts off ... inducements from abroad to corruption, negotiation, and war.”18
Just five years later (1833), in his celebrated constitutional commentary, Justice Joseph Story contrasted natural-born citizen with naturalized citizen19—the latter being one born a citizen of a different country who later becomes a U.S. citizen. This contrast, of course, later appeared also in Section 1 of the Fourteenth Amendment. Again, blood rights are ignored.
So the question boils down to whether blood rights are encompassed in the common-law meaning of natural-born citizen. The 1790 federal statute cannot affect the meaning of the constitutional words in Article II, which took effect in 1789. In fact, the enactment of the 1790 statute suggests that the common-law meaning was explicitly being changed.
Under a well-accepted canon of construction, constitutional or statutory words and phrases with an accepted common-law meaning are presumed to bear their common-law meaning—unless explicitly redefined.20
If English law as it was received in the United States was as Blackstone defined it—only children whose fathers are natural-born subjects can themselves be natural-born subjects—then someone whose mother conferred the blood rights wouldn’t be eligible under Article II, unless that eligibility was amended by the Equal Protection Clause. We will turn to that point after ascertaining the common-law meaning of natural-born subject when the Constitution was ratified in 1789.
Much depends on the two statutes from 1708 and 1731. The first, entitled “An Act for Naturalizing Foreign Protestants,” was broad: “[T]he Children of all Natural-born Subjects, born out of the Ligeance of her Majesty, her heirs and Successors, shall be deemed, adjudged and taken to be Natural-born Subjects of this Kingdom, to all Intents, Constructions, and Purposes whatsoever.”21 Note the word naturalization in the title. The phrase natural-born subjects is used in each clause of the statute, not just for blood rights. So all these people were considered subjects by “naturalization.”
By 1731, the meaning of this provision had been called into question. Parliament enacted another statute narrowing the broad sense of the original. The preamble explicitly stated its interpretive purpose: “WHEREAS ... some Doubts have arisen upon the Construction of the said recited Clause in the said Act ... relating to Children of natural born Subjects,” Parliament wanted to “prevent any Disputes touching the true Intent and Meaning thereof.”22 The new provision restricted the meaning to children of father-subjects, thus excluding mother-subjects:
[A]ll children born out of the Ligeance of the Crown of England, or of Great Britain, or which shall hereafter be born out of such Ligeance, whose fathers were or shall be natural born Subjects of the Crown of England, or of Great Britain, at the time of the Birth of such Children respectively, shall and may, by virtue of the said recited Clause in the said Act of the Seventh Year of the Reign of her said late Majesty, and of this present Act, be adjudged and taken to be, and all such Children are hereby declared to be natural born Subjects of the Crown of Great Britain, to all Intents, Constructions, and Purposes whatsoever.23
This “deeming clause” might be taken to create a fiction: you’re “taken to be” and “declared to be” a natural-born citizen even if you’re not. Hence the reference in the titles of the statutes to “naturalization.”
A further question arises: to what extent was a 1708 or 1731 statute incorporated into American law? The answer is that they are entirely applicable. According to the U.S. Supreme Court in 1831: “These statutes being passed before the emigration of our ancestors, being applicable to our situation, and in amendment of the law, constitute a part of our common law.”24 In his 1828 Commentaries on American Law, James Kent had used virtually the same words.25
Were these statutes “applicable to our situation”? Apparently. After all, the 1790 federal statute had likewise restricted blood rights to those born of father-citizens, just as the British statute had restricted them to father-subjects. But the federal statute had a further restriction: only father-citizens who had been resident in the United States could confer blood rights.
So a further question arises: Are citizens by blood rights to be considered “naturalized,” as the title of the 1708 statute suggests? The 18th-century view was that “[t]he title of a Statute is not to be regarded in construing it, because it is no part thereof.”26 That’s because Parliament never voted on titles—just on the words of the statutes themselves. The titles were added later by printers.
Hence no stock should be put in the title—whether it’s the title of the 1708 statute or the similarly titled federal statute of 1790. Both referred to naturalization, but the common-law rule of disregarding titles applied to both.
Finally, then, the question boils down to whether blood rights confer natural-born status or merely cause “automatic naturalization.” Note the broad words of the statutory declaration that became part of American common law: “are hereby declared to be natural born Subjects ... to all Intents, Constructions, and Purposes whatsoever.” That language might seem determinative: natural-born includes someone who becomes a citizen by blood rights. That was the state of the law in 1789.
But the automatic-naturalization argument has some force. It is not uncommon in legal literature to see references to a foreign-born child of a citizen as “naturalized at birth.” The words naturalize and naturalization are common in this context. Thus Sir Francis Bacon argued in 1607: “By the statute of 25 Edw. III which, if you believe Hussey, is but a declaration of the common law, all children born in any parts of the world, if they be of English parents continuing at that time as liege subjects to the King, and having done no act to forfeit the benefit of their allegiance, are ‘ipso facto’ naturalized.”27
Hence the constitutionality of the restriction to father-citizens wouldn’t come into play. Blood rights would be a matter of naturalization at birth. So the “conventional wisdom” cited at the outset—the idea that there are three modes of acquiring citizenship—might be incorrect. At common law and at the time of the Constitution’s ratification, there were two modes: birth within the nation (jus soli) and naturalization (of which blood rights, or jus sanguinis, is a subset). On this view, a foreign-born child of a U.S. citizen has been naturalized at birth—but naturalized, to be sure.
But Article II doesn’t disqualify someone “naturalized at birth.” It says “natural-born citizen.” And as we have seen, at common law a foreign-born child of a father-subject is considered for “all purposes whatsoever” a natural-born subject. That should be conclusive.
Would the ancient male-only restriction disqualify a foreign-born presidential candidate whose mother alone was a U.S. citizen? Seemingly (and surprisingly) yes. The Supreme Court has never struck down on equal-protection grounds a statute that accords differential treatment for blood rights on the basis of parental gender. As recently as 1961, the Court held that an 1855 federal statute basing blood rights solely on the father’s citizenship had been valid until the statute was changed in 1934.28 A man born in Italy to an American mother and Italian father sought to prove he was an American citizen through his mother.29 Two statutes applied. One stated: “All children heretofore born or hereafter born out of the limits and jurisdiction of the United States, whose fathers were or may be at the time of their birth citizens thereof, are declared to be citizens of the United States; but the rights of citizenship shall not descend to children whose fathers never resided in the United States.”30 The other provided: “children of persons who now are, or have been citizens of the United States, shall, though born out of the limits and jurisdiction of the United States, be considered as citizens thereof.”31 The Court noted that the word “persons” could be read to include both citizen mothers and fathers.32 But when Congress changed the law in 193433 and extended citizenship to the foreign-born children of mothers, it expressly stated that the existing law was reversed.34 For this reason, the Court concluded that until then, only fathers could convey citizenship to their children.35 So blood rights through the male parent alone were embodied in a statute passed before the Fourteenth Amendment was ratified.
Nowhere did the Court mention the Equal Protection Clause or the Fourteenth Amendment. To some judges today, that fact suggests that the point was neither briefed nor argued, and it wasn’t considered by the Court. This might mean that the decision cannot be said to hold that such a statute doesn’t violate equal protection. The opinion was per incuriam (to use a favorite phrase of English jurists): it was written in ignorance of controlling law. But originalists would conclude quite to the contrary. They would say that the Court’s silence on the point shows that because nobody thought it might be unconstitutional, it was considered fully constitutional for a long time before and after the ratification of the Fourteenth Amendment. The eight members of the U.S. Supreme Court who joined in the 1961 opinion (all but William O. Douglas, who dissented without opinion) were no dummies. They’d have brought up equal protection if it were a pertinent point.
As things stand today, the Equal Protection Clause doesn’t forbid all gender differentiations. The fact that a federal statute to determine blood-rights citizenship clearly makes distinctions based on a parent’s gender does not necessarily make the statute unconstitutional. The current statute36 imposes a proof-of-paternity requirement on a person born out of wedlock and abroad to a citizen father and alien mother before the person can establish a blood right to citizenship.37 There is no similar requirement of a person born to a citizen mother.
In two cases, the Court has explained that the statute is not unconstitutional because unwed male and female parents are not similarly situated: the maternal relationship is known at birth, but the paternal relationship must be actively proved.38 And in 2001, the Court emphasized that Congress could reasonably require proof that a citizen parent and child had at least the opportunity to develop a relationship, which would presumably include shaping the child’s ties and allegiance to the United States.39 Giving birth automatically provides a mother with opportunity, but nothing assures a father of that opportunity.40 The Court concluded that “[f]athers and mothers are not similarly situated with regard to the proof of biological parenthood.”41 And “[t]o fail to acknowledge even our most basic biological differences—such as the fact that a mother must be present at birth but the father need not be—risks making the guarantee of equal protection superficial, and so disserving it.”42
What is important about these more recent cases (1998, 2001) is that they analyze the differential treatment against the traditional rational-basis standard for assessing equal protection. The state must have a rational basis for its differential treatment. And ultimately the answer to what the Supreme Court would say today probably lies in that fact.
We have seen that the law in 1789 treated mother-citizens less favorably than father-citizens in conferring citizen rights when a child is born abroad. We have seen that in 1961, the Supreme Court upheld just this type of differential treatment. Was there a rational basis for the distinction? Not in the modern era of the equal-protection analysis: The only basis for the differential treatment was that we lived in a patriarchal society in which paternal lines of succession were considered more important than maternal ones. Judged by current standards of equal protection, no such discriminatory difference would be upheld by the Supreme Court today. But an originalist interpretation would almost certainly be to the contrary.
All in all, it seems highly likely that the Supreme Court would today hold that the foreign-born child of a mother-citizen is eligible for the Presidency under Article II of the Constitution.
 Black’s Law Dictionary 298 (Bryan A. Garner ed., 10th ed. 2014) (defining natural-born citizen as a “person born within the jurisdiction of a national government”).
 2 The Oxford International Encyclopedia of Legal History 1–2 (Stanley Katz ed., 2009).
 See Hennessy v. Richardson Drug Co., 189 U.S. 25, 34–35 (1903) (recognizing the identical nature of citizen [for democracy] and subject [for monarchy]).
 1 William Blackstone, Commentaries on the Laws of England 354 (1765).
 Id. at 361.
 Act of 26 Mar. 1790, ch. 3, § 1, 1 Stat. 103, 104.
 1 The Laws of the United States of America 87 (1796).
 3 The Laws of the United States of America 163, 165 (1796).
 Act of 14 Apr. 1802, § 4 (2 Stat. 155) (emphasis added).
 R.S. § 1993 (substantially reenacting Act of 10 Feb. 1855 [10 Stat. 604]) (emphasis added).
 H.R. Rep. No. 131, 73d Cong., 1st Sess., at 2; Sen. Rep. No. 865, 73d Cong., 2d Sess., at 1.
 Montana v. Kennedy, 366 U.S. 308, 313 (1961) (interpreting Act of 14 Apr. 1802, 2 Stat. 155, codified at R.S. § 2172).
 U.S. Const. amend 14, § 1.
 Rogers v. Bellei, 401 U.S. 815, 830 (1971).
 2 James Kent, Commentaries on American Law *274 (1828; Oliver Wendell Holmes ed., 12th ed. 1873).
 3 Joseph Story, Commentaries on the Constitution of the United States § 1473, at 332 (1833) (using natural-born citizen and naturalized citizen in consecutive sentences by way of contrast).
 See Antonin Scalia & Bryan A. Garner, Reading Law: The Interpretation of Legal Texts 320–21 (2012).
 4 The Statutes at Large Containing All the Publick Acts of Parliament 186 (1735).
 6 The Statutes at Large Containing All the Publick Acts of Parliament 299 (1734).
 Doe ex. dem. Patterson v. Winn, 30 U.S. 233, 241–42 (1831).
 1 James Kent, Commentaries on American Law *473 (Oliver Wendell Holmes ed., 12th ed. 1873).
 4 Matthew Bacon, A New Abridgment of the Law 645 (1759). See also Antonin Scalia & Bryan A. Garner, Reading Law: The Interpretation of Legal Texts 221 (2012) (citing Lord Coke and later judges to the same effect).
 Francis Bacon, “The Argument of Sir Francis Bacon, Knight, His Majesty’s Solicitor-General, in the Case of the Post-Nati of Scotland,” in 2 The Works of Francis Bacon 166, 171 (Basil Montagu ed., 1887).
 Montana, 366 U.S. at 312.
 Id. at 310 (citing Rev. Stat. § 1993 (1874), re-enacting § 4 of an Act of April 14, 1802 (2 Stat. 155)).
 Id. (citing Rev. Stat. § 2172 (1874), re-enacting § 1 of Act of 10 Feb. 1855 (10 Stat. 604)).
 48 Stat. 797.
 Montana, 366 U.S. at 312.
 8 U.S.C. § 1409.
 8 U.S.C. § 1409(a).
 Miller v. Albright, 523 U.S. 420, 434, 436–37 (1998); Tuan Anh Nguyen v. I.N.S., 533 U.S. 53, 62–64 (2001). Miller v. Albright, 523 U.S. 420, 443–44 (1998)
 Miller, 523 U.S. at 439–40, 441; Nguyen, 533 U.S. at 67.
 Nguyen, 533 U.S. at 64–66, 67.
 Id. at 63. See also Miller, 523 U.S. at 445 (“The biological differences between single men and single women provide a relevant basis for differing rules governing their ability to confer citizenship on children born out of wedlock in foreign lands.”).
 Nguyen, 533 U.S. at 73.