See Parts I, II, and especially Part III (the earlier Blackstone misquote) below.
Great Officers of State, Subordinate Magistrates, and “Principal Officers”
Now we come to a remarkable confusion in the Seila Law amicus brief: The English “principal secretary” (i.e., a cabinet member) is not the equivalent of the U.S. Constitution’s “principal officer” (which the amicus extends to the CFPB director and beyond). It’s a revealing historical confusion in their argument.
Blackstone’s categories simply do not track our modern American categories, and there is still confusion about how many hundreds, or perhaps after Lucia v. SEC (2018) and Arthrex (2021),  now thousands of administrative officers are “principal officers.” Blackstone was referring more to the dozen or so highest officers in England – Secretaries of State and the like – and not anything close to the legions of principal officers in the U.S. Constitutional system of Article II.
It helps to put Chapter Nine in context, compare the word “secretary” elsewhere in the Commentaries, and then read the full three paragraphs introducing this chapter on “subordinate magistrates.” Book One of the Commentaries is titled “The Rights of Persons,” but the book starts more about the powers of government officials. Chapter Two is on Parliament, followed by Chapter Three on the King, reflecting Blackstone’s emphasis on parliamentary supremacy. After a chapter on the royal family, Chapter Five is “Of the Councils Belonging to the King,” followed by chapters on the king’s duties, prerogatives, and revenue. Picking up after Chapter Five on the councils is Chapter Nine, “Of Subordinate Magistrates.” They seem to be constructed as complements: Chapter Five lists specific high councils and offices: Parliament, the aristocratic Peers, the judges and courts of law, and then “the council,” or the privy council. Blackstone explained that the privy council had grown too large, so Charles II set it back to thirty in 1679, “whereof fifteen were to be the principal officers of state,” ex officio, “and the other fifteen were composed of ten lords and five commoners of the king’s choosing.” The number had increased since then, but apparently from the other descriptions in the Commentaries, this was due to the increase of additional appointments of lords and commoners, not an increase in secretaries.
First, Joseph Chitty, the commentator on the 1826 edition of the Commentaries, added a note to this paragraph on the privy council, describing its “offices of state” or “great officers” as limited to “the cabinet.” Chitty listed roughly fourteen officers, including “the lord-high chancellor,” “the first lord of the treasury,” and “the secretaries of state for the home department, colonies, and foreign affairs.” This note suggests that there were only a handful of “high officers” or “principal secretaries.” Blackstone himself used the word “secretaries” in the context of the highest offices, the “secretaries of state” on the same level as the judges of King’s Bench and “the attorney and solicitor general.” The evidence suggests that “great officers of the states” and “principal secretaries” were comparable to the American “department heads,” i.e., secretaries of departments and members of the cabinet. Even if Blackstone were claiming that the king had complete removal power over these “great officers,” it was not analogous to a removal power over any principal officer in an American context.
Speaking of context, it helps to read the other sentences around this single misinterpreted sentence to clarify who were the “great officers of state.” In the opening paragraph preceding the one we have been focusing on, Blackstone writes, “[We] are now to proceed to inquire into the rights and duties of the principal subordinate magistrates” (italics in the original). Some of those “principal subordinate magistrates” would have protection against removal, and did not serve at the king’s pleasure. It seems even more plausible that “principal subordinate magistrates” might track the principal officers mentioned in Article II, but who were not “department heads,” as mentioned in Article II. If so, then Blackstone provides evidence that “principal subordinate magistrates” included coroners, who had mixed executive and judicial functions, and were protected from removal. It seems plausible that other “principal subordinate magistrates” in this section did not serve at the king’s pleasure. Did Blackstone mean “principal” in the sense of their power or in the sense of being the “main example” or “primary example”? This category of “principal subordinate” officers would include those with protections against removal. One cannot claim from these paragraphs that they establish a rule in favor of removal protections against the king, but nor can one claim they establish a rule in favor of royal removal over high-level officers below the cabinet level.
Blackstone wrapped up the introduction by listing the officers that will be investigated: “sheriffs, coroners, justices of the peace, constables, surveyors of highways, and overseers of the poor.” And then he listed the topics of inquiry: “first, their antiquity and origin; next, the manner in which they are appointed and may be removed; and, lastly, their rights and duties.” Indeed, Blackstone focused on appointment and removal in this chapter, with different limits on removal. Blackstone reflects a range of removal rules and a lack of a default rule. Blackstone’s focus on the specific case-by-case circumstances of offices, tenure, and removal suggests that the removal power operated on a case-by-case basis, and no general rule of executive removal. For more in-depth analysis of Blackstone, see Daniel Birk’s “Interrogating the Historical Basis for the Unitary Executive,” Stanford Law Review, 202 & passim, and Manners & Menand, supra.
The point is not the Blackstone’s Chapter Nine clearly refuted a unitary executive claim that 18th-century England’s rough equivalent of Article II “principal officers” served at the king’s pleasure; the point is that Chapter Nine is unsurprisingly unclear on these terms and cannot be relied upon to support such a claim in the Seila Law brief. It was an error to rely on Blackstone at all for such broad claims beyond the highest cabinet-level Secretaries and “great officers of state.”
 See U.S. v. Arthrex (2021); Lucia v. SEC, 138 S. Ct. 2044, (2018).