CAGAYAN de Oro City— The Senate impeachment court has scrapped the fixed 16-vote requirement for convicting Vice President Sara Duterte, opening a constitutional dispute over which senators should be counted when applying the two-thirds rule.

The impeachment court voted 13-1 on Sept. 23, with six senator-judges not participating, to overturn Presiding Officer Francis Escudero’s earlier ruling that 16 votes were required based on the Senate’s full 24-member composition.

Under the new ruling, the two-thirds requirement will instead be computed from senators who are legally and factually capable of participating when the court eventually votes on Duterte’s guilt or acquittal.

The ruling does not set a permanent replacement for 16 votes. If, for example, 20 senators are determined to be eligible to participate, two-thirds would be 13.33, which the court said must be rounded up to 14 votes.

The change has triggered competing constitutional interpretations.

The Senate majority says it did not lower the Constitution’s two-thirds requirement. Instead, it changed the basis from which the two-thirds fraction is computed.

The defense argues that the Constitution refers to “all the Members of the Senate” and that the Senate’s constitutionally fixed membership is 24. Under that interpretation, two-thirds remains 16 regardless of a senator’s absence, detention or inability to participate.

WHAT THE CONSTITUTION SAYS

Article XI, Section 3(6) of the 1987 Constitution states that no person may be convicted in an impeachment trial without the concurrence of two-thirds of all the Members of the Senate.

Article VI, Section 2 provides that the Senate is composed of 24 senators.

That language formed the basis of Escudero’s earlier 16-vote ruling.

The defense has also cited Bayan v. Zamora, in which the Supreme Court treated 24 as the relevant Senate membership for a two-thirds vote on treaty concurrence, even though there were only 23 incumbent senators at the time.

Defense lawyer Michael Poa argued that absence or non-participation does not create a vacancy and therefore should not automatically reduce the constitutional denominator.

The defense also argued that senators who are absent could still review the trial record, transcripts and evidence before rendering judgment.

THE OTHER SIDE: WHO CAN ACT AS AN IMPEACHMENT JUDGE?

House prosecutor Chel Diokno offered a different reading.

He argued that while the Constitution requires two-thirds, the question is “two-thirds of how many?”

The prosecution's position is that the relevant denominator should account for senators who are legally capable of performing the functions of an impeachment judge — including taking the required oath, hearing and examining evidence, deliberating and rendering judgment.

The Senate ultimately adopted that approach in its Sept. 23 ruling.

The court said senators who are detained, suspended or otherwise legally restrained from performing their functions, physically or medically incapacitated, beyond the Senate’s coercive processes, or similarly situated may be excluded from the denominator.

THE NUMBER CAN CHANGE — BUT SO CAN THE MATH FOR BOTH SIDES

The dispute has often been framed as whether the Senate lowered the number of votes needed to convict Duterte.

But the new formula affects the arithmetic on both sides.

With 24 senators as the denominator, two-thirds requires 16 votes.

With 20, two-thirds is 13.33, requiring 14 votes to convict.

But under the same 20-member denominator, seven votes would be enough to prevent conviction, compared with nine votes under a 24-member denominator.

The prosecution itself acknowledged during oral arguments that changing the denominator does not automatically favor conviction because the mathematical effect applies to both the votes needed for conviction and those needed to prevent it.

MONSOD BACKS THE SENATE'S INTERPRETATION

Constitutional framer Christian Monsod later backed the Senate's decision, saying the denominator can change when senators are unable to sit as impeachment judges.

“They are correct. The denominator can be changed,” Monsod said in an interview with Storycon on One News on Sept. 23.

Monsod specifically pointed to detained senators Jinggoy Estrada and Rodante Marcoleta, arguing that their inability to participate should affect the computation.

Former Senate President Franklin Drilon has likewise said the two-thirds threshold should be based on senators who are available and subject to the Senate’s compulsory jurisdiction.

But their views are legal interpretations, not a final Supreme Court ruling on the issue.

THE LEGAL QUESTION REMAINS

The Senate's ruling is limited to Duterte's impeachment trial and was declared pro hac vice, or applicable only to the present case. Escudero said it would not constitute a binding precedent for future impeachment proceedings.

That leaves the central constitutional question unresolved:

Does “two-thirds of all the Members of the Senate” mean two-thirds of the Senate’s full constitutional membership, or two-thirds of the senators who are legally and factually capable of performing their functions as impeachment judges?

The answer will determine the actual number of votes required when the Senate eventually decides Duterte’s impeachment case.

For now, the Senate has changed the denominator, not the constitutional fraction.

Whether that interpretation is consistent with the Constitution is the issue that remains open to legal challenge.