What makes someone a &quot;principal officer of an executive department&quot;?
<p><a href="https://constitution.congress.gov/browse/amendment-25/section-4/" rel="nofollow noreferrer">§4 of the 25th amendment</a> makes reference to &quot;a majority of either the principal officers of the executive departments or of such other body as Congress may by law provide&quot; – Congress has not provided anything else. <a href="https://www.law.cornell.edu/uscode/text/5/101" rel="nofollow noreferrer">5 USC 101</a> lists the &quot;executive departments&quot;. Art II § 2 of the Constitution says that the president</p>
<blockquote>
<p>shall nominate, and by and with the Advice and Consent of the Senate,
shall appoint Ambassadors, other public Ministers and Consuls, Judges
of the Supreme Court, and all other Officers of the United States,
whose Appointments are not herein otherwise provided for</p>
</blockquote>
<p>It is reasonable (but not self-evident) that having been nominated to be a principal officer of, e.g., the Dept. of Justice does not thereby make you one.</p>
<p>What legal precedent can be called on to decide if an acting department head &quot;counts&quot; as a principal officer for purposes of the 25th Amendment §4, either for determining what number constitutes a &quot;majority&quot;, and for determining whose written declarations are to be considered?</p>

<p>The question has no definitive resolution other than the authorities cited and some other related authorities such as the protocol rules of the Secretary of State for diplomatic purposes and the Presidential succession statute. It has never been litigated any reasonable interpretations of the the constitution and relevant law could be argued. There is also some case law under the appointments clause regarding which departments count as principal departments.</p>
<p>There is a broad consensus regarding the existence of 15 principal departments of the United States government and which departments those 15 departments are in practice.</p>
<p>I would say that the majority view is that the highest ranking person in each department is the principal officer of that department (which is provided for by statute in the event of vacancies) but there is also an argument that only the Congressional ratified and Presidentially nominated Secretary of a department (and the Attorney General in the Justice Department similarly appointed) count.</p>
<p>In the event of a dispute, either Congress or a court could resolve the issue depending upon how the issues ended up being presented for a decision. If asked, the White House Counsel would render a formal opinion that would be binding upon all members of the Executive Branch.</p>
<p>Triller novel writer Tom Clancy has explored some of the scenarios as have other writers in the same genre, but since the 25th Amendment has never been invoked in this manner, there is no definitive answer or even a non-judicial precedent to provide us with guidance on the question.</p>

<h2>There is only one “principal officer” of each <a href="https://en.wikipedia.org/wiki/United_States_federal_executive_departments" rel="nofollow noreferrer">executive department</a></h2>
<p>There are currently 15 of these men (funny that they’re all men, isn’t it): their names and photos are in the linked article. They become the principal officers after being confirmed by Congress.</p>
<p>A person acting in that capacity is <em>not</em> a principal officer. The 25th amendment has never been triggered so there is no case law to decide if they can exercise the functions if they are merely acting or what a majority means if some of the positions are vacant.</p>

united-states constitutional-law