MANILA, Philippines — What looked like simple constitutional arithmetic has turned into one of the most consequential procedural disputes in Vice President Sara Duterte’s impeachment trial.
Retired Chief Justice Hilario Davide Jr. told the Senate impeachment court that the constitutionally required two-thirds vote for conviction should not automatically be calculated from all 24 Senate seats. Instead, he argued that the denominator should consist of senators who are legally and physically qualified to participate and vote in the proceeding.
Davide made the argument in a written memorandum submitted as amicus curiae, or friend of the court, on Wednesday, September 16. His memorandum was read into the record because he did not appear personally. Retired Chief Justices Artemio Panganiban and Reynato Puno and retired Associate Justice Adolfo Azcuna appeared before the impeachment court to offer their own interpretations.
The question sounds narrow, but its practical significance is substantial:
Does “two-thirds of all the Members of the Senate” always mean 16 votes — or can the required number change when some senator-judges cannot legally or physically take part?
The Constitution supplies the fraction. The Senate now has to decide what the denominator means under the unusual circumstances confronting the current trial.
What the Constitution Actually Says
Article XI, Section 3(6) of the 1987 Constitution gives the Senate the sole authority to try and decide impeachment cases and states that no impeached official may be convicted without the concurrence of “two-thirds of all the Members of the Senate.”
The Constitution separately provides that the Senate is composed of 24 senators. Under the conventional calculation, two-thirds of 24 equals 16 votes.
That was the interpretation Senate impeachment court Presiding Officer Francis “Chiz” Escudero adopted when Duterte’s trial opened on July 6.
But Senator-Judge Erwin Tulfo later asked the court to reconsider the ruling because several senator-judges have not been participating in the proceedings and, in some cases, are beyond the Senate’s ability to compel attendance. Escudero treated Tulfo’s intervention as an appeal or motion to reconsider his earlier ruling.
Importantly, the dispute concerns how the conviction threshold should be computed. It does not resolve whether Duterte is guilty or innocent of any impeachment article. Senator Bam Aquino made that distinction when the issue was raised, saying the threshold question should be treated separately from the merits of the case.
Why the ‘Hard 16’ Has Become Controversial
The problem emerged because four senator-judges have not been regularly taking part in the trial under very different circumstances.
Reporting ahead of the amici hearing identified Loren Legarda, who was on medical leave abroad; Ronald “Bato” dela Rosa, who has been absent while facing an International Criminal Court arrest warrant; and Jinggoy Estrada and Rodante Marcoleta, who have been detained in connection with separate plunder cases.
The criminal allegations involving detained senators remain subject to their respective legal proceedings and should not be confused with the impeachment case against Duterte.
Tulfo’s concern is mathematical as well as constitutional.
If all 24 senators must always be included in the denominator, a senator who is unable to participate could effectively make reaching the two-thirds threshold more difficult without ever casting an actual vote. Tulfo previously described that possibility as potentially turning absences into practical “no” votes.
But whether that consequence permits the Senate to reinterpret the phrase “all the Members” is precisely what the impeachment court is now debating.
Davide: Count Senators Who Are Qualified to Vote
Davide’s answer is that 24 should not necessarily be treated as an unchangeable denominator.
In his memorandum, he argued that senators prevented from acting because of legal or physical impediments should not automatically be included when calculating the constitutional two-thirds requirement.
He specifically pointed to circumstances involving senators who are detained, abroad, suspended or whose whereabouts are unknown.
Davide argued that the Constitution’s framers did not specifically debate the precise meaning of the phrase “all the Members of the Senate” under circumstances like those now confronting the impeachment court.
His interpretation would therefore mean that 16 is not necessarily the required number in every factual situation.
The precise threshold would depend on which senators the impeachment court ultimately considers legally qualified to be included in the voting base.
That qualification is important: Davide’s position should not be simplified into a rule that every senator who misses a hearing automatically disappears from the denominator. His argument concerns senators who cannot validly participate because of the kinds of legal or physical impediments identified in his memorandum.
Davide Looked to a 1949 Senate Crisis
One of the precedents raised in the debate is the Supreme Court’s 1949 ruling in Avelino v. Cuenco.
That dispute concerned the Senate presidency and whether there was a valid quorum when only 12 senators were present. At the time, one of the 24 senators was hospitalized and another was abroad. Later Supreme Court opinions discussing Avelino recount that the Court had to determine whether those circumstances affected the number needed for Senate action.
Davide considers the case relevant by analogy to the impeachment dispute.
But he also acknowledged that Avelino is not directly controlling, because it dealt with a quorum and the election of a Senate president rather than the constitutional vote required to convict an impeached official.
That distinction is crucial.
The current question is not merely whether enough senators are present for the Senate to conduct business.
It concerns a separate constitutional clause specifically requiring the concurrence of two-thirds of all Senate members before an impeached official can be convicted.
Panganiban Also Challenged the Idea of a Fixed 16
Davide was not alone.
Retired Chief Justice Artemio Panganiban argued that the constitutional requirement should not be reduced automatically to a permanent mathematical formula of 16 votes.
Panganiban emphasized the importance of senator-judges actively participating in the proceedings and independently evaluating evidence before exercising their adjudicative responsibility.
His argument focuses not only on physical presence but on the nature of impeachment itself.
Senators sitting in an impeachment court are expected to assess evidence, hear arguments and exercise judgment before voting. For Panganiban, the court must therefore consider whether a senator who did not meaningfully participate should nevertheless be treated exactly the same as one who did.
That raises a second issue beyond the denominator:
Can a senator who barely or never participated in the trial still cast the final vote?
The impeachment court expressly asked the amici to address that question as well.
Puno Says the Constitution Used a Fraction for a Reason
Retired Chief Justice Reynato Puno also rejected treating 16 as automatically fixed under every circumstance.
He argued that Article XI, Section 3(6) deliberately uses the fraction two-thirds rather than specifying the number 16.
Puno told the impeachment court that the constitutional provision should be interpreted contextually, including consideration of circumstances such as death, resignation, expulsion or legal incapacity of individual senators.
His reasoning differs in detail from Davide’s and Panganiban’s, but all three broadly challenged the proposition that the constitutional threshold must remain 16 regardless of changes affecting who can legally participate.
That still does not make their position the ruling of the impeachment court.
The amici advise the senator-judges; they do not decide the issue themselves.
Azcuna Takes the Opposite View: All 24 Still Count
Retired Associate Justice Adolfo Azcuna, himself a member of the 1986 Constitutional Commission that drafted the present Constitution, offered the principal competing interpretation.
Azcuna argued that all sitting senators should remain part of the denominator, meaning the two-thirds requirement remains 16 votes in a 24-member Senate.
He maintained that the phrase “all the Members of the Senate” was deliberately chosen and should not be rewritten simply because individual senators are absent or unable to attend.
Azcuna also took the position that the issue of whether a senator who failed to participate substantially can cast a final vote is an internal matter on which the Senate may adopt its own rules.
His interpretation reflects the strongest textual argument for keeping the original threshold:
The Constitution says all members, and the Constitution itself establishes a 24-member Senate.
The competing view is that applying those words without regard to legal incapacity or other extraordinary circumstances could produce a result inconsistent with the functioning of an impeachment court.
The Senate must now choose between — or potentially reconcile — those approaches.
Even the Constitution’s Framers Disagree
The disagreement between Davide and Azcuna is especially notable because both served on the 1986 Constitutional Commission that drafted the 1987 Constitution.
Davide also brings another unusual perspective: he presided over the impeachment trial of former President Joseph Estrada when he was chief justice.
But historical involvement does not make either former justice’s interpretation legally binding.
Their disagreement illustrates why the issue cannot simply be settled by saying “the framers intended” one particular result when surviving framers themselves can interpret the language differently decades later.
The text remains the starting point; the Senate impeachment court must determine how it applies to the current factual circumstances.
The House Prosecution Is Preparing to Argue for a Smaller Voting Base
The House prosecution initially said it would leave the threshold question to the senator-judges.
But lead prosecutor Rep. Gerville “Jinky Bitrics” Luistro said on September 16 that the prosecution would now advocate an interpretation under which the threshold would be easier to reach after the impeachment court scheduled formal oral arguments.
Other prosecution representatives subsequently stressed that the amici hearing did not amount to vindication for their side and that the prosecution would respect whatever threshold the Senate impeachment court ultimately adopts.
Duterte’s defense, meanwhile, had previously declined to publicly commit itself to a substantive position before the scheduled arguments, saying it wanted to hear the constitutional discussion first. Defense spokesperson Michael Poa confirmed that the team had selected a representative for the September 23 arguments but had not publicly identified that person.
September 23 Is the Next Critical Date
The amici hearing does not settle the matter.
The Senate impeachment court has scheduled oral arguments for September 23, when the House prosecution and Duterte’s defense will formally argue their positions on the voting threshold. The senator-judges are then expected to vote on whether to retain or modify Escudero’s original 16-vote ruling.
Escudero himself is expected not to cast another vote on the appeal because his original ruling already established his position, according to impeachment court spokesperson Reginald Tongol.
Until that process is completed, 16 remains the existing ruling.
Davide’s memorandum does not itself lower the threshold.
Panganiban’s and Puno’s positions do not lower it.
Azcuna’s disagreement does not permanently lock it at 16.
The impeachment court still has to decide.
Why This Procedural Fight Matters
The disagreement is not about replacing the constitutional two-thirds requirement. All sides in the current debate accept that fraction.
The dispute is over two-thirds of whom.
Under one interpretation, the Constitution establishes a full 24-member denominator, making 16 votes necessary regardless of absences.
Under the competing interpretation advanced in different forms by Davide, Panganiban and Puno, senators who cannot lawfully or meaningfully participate may have to be excluded before the two-thirds calculation is made.
The distinction could matter whenever an impeachment court operates with vacancies, legal incapacities, suspensions, prolonged absences or other extraordinary circumstances — not only in Duterte’s present case.
And that is why the September 16 hearing developed into something much larger than a debate over basic arithmetic.
The Constitution clearly says two-thirds. What the Senate has not yet finally decided is who belongs in the number being divided.
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