Senator-judges alongside the prosecution and defense panels listen as retired Supreme Court Chief Justices Artemio Panganiban, Reynato Puno, along with retired SC Associate Justice Adolfo Azcuna, offer their opinions on the constitutional voting threshold required in the Senate impeachment trial of Vice President Sara Duterte on September 16, 2026. Retired SC Chief Justice Hilario Davide Jr. also sent his opinion via a legal memorandum read by the Clerk of Court. (Courtesy: Senate of the Philippines / Senate PPA Pool via Lino Santos / AFP File Photo)
Three retired Supreme Court chief justices told the Senate impeachment court Wednesday that the 16 votes currently required to convict Vice President Sara Duterte are not necessarily fixed, while retired SC Associate Justice Adolfo Azcuna maintained that all 24 senators must be counted in determining the constitutionally required two-thirds vote.
The four former magistrates were invited as amici curiae, or friends of the court, to provide independent legal guidance as the impeachment court reviews Presiding Officer Senator-Judge Francis “Chiz” Escudero’s earlier ruling that 16 votes, or two-thirds of the full 24-member Senate, are required to convict Duterte.
Retired Chief Justices Hilario Davide Jr., Artemio Panganiban, and Reynato Puno said the threshold could change depending on which senators are legally qualified to participate and vote. Azcuna took the contrary position that the denominator must remain the entire sitting membership of the Senate.
Davide, who could not personally appear because he was recovering from a medical procedure, submitted a legal memorandum saying the two-thirds requirement should be computed based on senators qualified to vote rather than automatically on all 24 senators.
“Clearly then, the basis of computing the two-thirds must be the number of senators who are qualified to vote, not the 24 in the present Senate,” Davide said.
He said senators who had resigned or been expelled, were incapacitated, were outside Philippine jurisdiction or whose whereabouts were unknown, as well as those prevented by legal restraints from exercising their functions, should not be included in the computation.
Davide said the constitutional phrase “all the Members of the Senate” refers to living senators who are capable of exercising their powers and performing their duties and are not legally barred from doing so.
Panganiban acknowledged that two-thirds of the constitutionally prescribed 24-member Senate is mathematically 16, but said the calculation does not necessarily apply in every circumstance.
“Therefore, 24 multiplied by two-thirds is always 16 in the abstract. But not always in reality,” he said.
“Reality sometimes, Your Honors, changes the denominator in mathematics,” Panganiban added.
(From left) Retired Supreme Court Associate Justice Adolfo Azcuna with retired Chief Justices Artemio Panganiban and Reynato Puno serve as amici curiae or ‘friends of the court’ during Wednesday’s proceedings at the impeachment trial. (Courtesy: Senate of the Philippines)
‘Constitution specified a fraction’
Panganiban said the two-thirds vote should be based on active participation in the impeachment proceedings, questioning whether senators who are abroad, in hiding, legally detained, sick or hospitalized and unable to examine evidence and hear testimony should still be allowed to cast a final vote.
Puno likewise rejected a strictly literal reading that would make the 16-vote threshold fixed and immutable. He noted that the Constitution specifies a fraction—two-thirds—rather than an absolute number.
“By using two-thirds, the number of votes to convict will have to move depending on certain factors,” Puno said.
He favored a contextual and functional interpretation that would allow the impeachment court to determine whether senators who are dead, resigned, expelled or legally incapacitated should be counted.
Puno also said the 1949 Supreme Court ruling in Avelino vs. Cuenco could provide guidance on determining which members should be counted, although he acknowledged that the case, which involved Senate quorum and a member beyond the chamber’s coercive jurisdiction, was not a perfect precedent for the impeachment issue.
Azcuna disagreed, maintaining that the phrase “all the Members of the Senate” encompasses the entire sitting membership.
“As long as they are members of the Senate, they constitute the denominator in computing the threshold of two-thirds. Because all means all,” Azcuna said.
He argued that allowing the denominator to fluctuate depending on participation could weaken the supermajority safeguard in the impeachment process.
“A threshold must be fixed, not variable. It must be determinable from the start,” Azcuna said.
Azcuna said the two-thirds requirement was intended to require broad consensus for conviction rather than allow a temporary legislative majority to remove an impeachable official.
Different views on participating senator-judges
The four former magistrates also differed on whether senator-judges who missed or did not substantially participate in the trial may still cast a final vote.
Panganiban emphasized active participation and independent evaluation of the evidence, while Puno and Azcuna said senator-judges could evaluate the evidence through the trial record even without personally observing every witness.
Davide said a senator-judge who never attended or performed any duties in the trial should be considered a nonparticipant, although failure to question witnesses alone would not establish nonparticipation.
The threshold issue arose after Senator-Judge Erwin Tulfo sought clarification on who should be counted among “all the Members of the Senate” when some senator-judges are unable to participate in the proceedings.
Escudero’s ruling requiring 16 votes remains in effect unless the impeachment court overturns it. The Senate is scheduled to hear oral arguments from the prosecution and defense on the issue on Sept. 23.
Palace ‘not taking a position’
Malacañang said Wednesday it would not take a position on the disputed threshold and would leave the matter to the Senate impeachment court.
Presidential Communications Office Undersecretary Claire Castro said the administration would not comment on whether the two-thirds requirement should be computed from all 24 senators or only those legally qualified to participate and vote.
“We will not give any opinion or any judgment regarding that. We will allow the Senate to determine what, in their view, is appropriate,” Castro said.
Castro said President Ferdinand Marcos Jr. would not interfere with the Senate’s determination.
“Whatever the threshold will be, the President will not interfere in that matter,” she said.
(Clockwise from top) Senator-judges Erwin Tulfo, Joel Villanueva, Kiko Pangilinan, Tito Sotto and Risa Hontiveros participate at the impeachment trial on September 16, 2026. (Courtesy: Senate of the Philippines)
VP open to elevating issues to SC
Vice President Duterte’s camp, meanwhile, said it was open to elevating issues arising from the impeachment proceedings to the Supreme Court if her constitutional rights are affected.
Duterte’s trial spokesperson, Atty. Michael Poa, said the defense participated in the amici curiae hearing “ad cautelam,” or out of an abundance of caution, to protect the Vice President’s rights.
Poa said any move to bring the matter before the Supreme Court would depend on whether the issue is justiciable and ripe for review, stressing that the defense would not seek judicial intervention merely to delay the trial.
“Of course, there’s always that possibility. If we see that the rights of our client, who is the respondent, the vice president, are being affected, it is possible that we could elevate the matter to the Supreme Court. We are just covering our bases,” Poa said.
He said the defense had not yet decided whether to seek Supreme Court intervention.
“It depends on the situation and our assessment of whether it is appropriate to elevate the matter to the Supreme Court and whether it is a justiciable issue. We will not go to the Supreme Court merely to cause trouble or delay the proceedings,” Poa said.
He said the defense respected the opinions of all four former magistrates regardless of whether they supported its position.
Prosecution taking ‘easier’ conviction threshold
The House prosecution, meanwhile, is expected to take a position that would make the conviction threshold easier to reach as the Senate impeachment court determines which senators should be counted in computing the two-thirds requirement.
House trial spokesperson Zia Alonto Adiong said the constitutionally required two-thirds vote should not necessarily translate into a fixed number, citing the positions presented by most of the amici curiae.
The disputed interpretation could affect the number of votes needed to convict Duterte. Until the impeachment court rules otherwise, however, Escudero’s 16-vote requirement based on the full 24-member Senate remains in effect.
Earlier, Senate Minority Leader Alan Peter Cayetano cautioned against changing conviction rules during the ongoing impeachment trial, emphasizing that the requirement of two-thirds of the Senate for conviction should be upheld.
Cayetano said changing the conviction requirement could set a dangerous precedent for future trials, affecting decisions for years to come.
“This impeachment court’s decision and how we conduct ourselves and whether we follow the rules or not will determine our destiny not only in the next two years, 10 years, maybe in the next 40 years,” he said.
Minority Senators Jinggoy Estrada and Rodante Marcoleta are currently absent from the chamber due to their detention related to separate non-bailable cases.
Senator Loren Legarda is also under investigation by the Office of the Ombudsman concerning a plunder complaint, while the location of Senator Bato dela Rosa remains uncertain following an arrest warrant issued against him by the International Criminal Court. —With Katrina Manubay and Charles Dantes