Sometimes history turns on wars, elections and revolutions.

Sometimes it turns on a denominator.

The Senate impeachment court is confronting what initially appears to be a question of arithmetic: How many votes are required to convict Vice President Sara Duterte?

Sixteen? Or can the number change if some senators are legally or practically unable to perform their duties as senator-judges?

Behind that deceptively simple calculation lies a constitutional question that could shape Philippine democracy long after the current protagonists have left office.

Article XI, Section 3(6) of the 1987 Constitution states: “No person shall be convicted without the concurrence of two-thirds of all the Members of the Senate.” With a full Senate of 24, the conventional calculation produces 16 votes. 

But what does “all the Members” mean when not all 24 can lawfully or meaningfully participate?

That is where arithmetic becomes constitutional law.

Two defensible readings

The case for 16 is straightforward.

Retired Supreme Court Justice Adolfo Azcuna, himself a member of the 1986 Constitutional Commission, told the impeachment court that as long as a senator remains a member of the Senate, that senator belongs in the denominator. In his formulation, “all means all.” 

There is considerable constitutional logic behind that position.

Impeachment is an extraordinary power. Conviction can remove an official elected nationally and may lead to disqualification from future public office. Requiring two-thirds of the entire Senate protects against removal by an ordinary political majority and forces a broader consensus before overturning an electoral mandate. 

But three former chief justices (CJs) offered a different interpretation.

CJs Hilario Davide Jr., Artemio Panganiban and Reynato Puno argued, through somewhat different reasoning, that 16 need not be immutable when senators are legally or functionally unable to discharge their duties. Davide maintained that the denominator should consist of senators qualified to vote. Panganiban emphasized meaningful participation in the trial. Puno noted that the Constitution deliberately uses the fraction two-thirds, rather than simply saying “16 senators.” 

Their concern is equally serious.

Suppose circumstances reduced the number of senators capable of participating to 16. If 16 votes remained necessary, conviction would require unanimity. Reduce the functional membership further and conviction could become mathematically impossible.

A constitutional mechanism expressly created to enforce public accountability could therefore be disabled by absence, incapacity, or legal impediment.

The ghost of 1949

Hovering over the controversy is Avelino v. Cuenco, the celebrated 1949 Senate quorum case.

There, the Supreme Court confronted a Senate in which one senator was abroad and beyond the chamber’s coercive reach. The controlling disposition treated the effective membership as 23 rather than 24 for purposes of determining a quorum.

But Avelino concerned a legislative quorum, not the constitutionally specified supermajority required to convict in impeachment. Even the amici curiae appearing before the Senate cautioned against mechanically transplanting the precedent into today’s controversy. 

That distinction matters.

Constitutional interpretation is rarely good medicine when precedent is prescribed for a disease it was never intended to treat. 

Dangerous precedent on either side

This is where the debate becomes larger than Sara Duterte.

A fixed denominator protects an accused official from a transient majority. But carried to its logical extreme, it could also create incentives for strategic absence or make conviction impossible when several senators cannot participate.

A variable denominator avoids paralysis. But it creates a different danger: Who determines which senators disappear from the denominator, and under what objective criteria?

Could detention reduce it? Suspension? Illness? Being overseas? Voluntary absence? Inhibition? Failure to attend enough trial days?

Those distinctions cannot safely be improvised when the final vote is already approaching.

A rule devised around the political circumstances of one accused official can become a constitutional weapon against the next.

Surviving a change of names

There is a useful test for the senator-judges: Erase the name Sara Duterte from the case. Imagine instead that the accused were a future president or vice president whom today’s prosecution passionately supported—or whom today’s defense vehemently opposed.

Would each senator still defend exactly the same interpretation?

That is the discipline constitutional government demands.

The Senate is exercising a power the Constitution expressly gives it alone: “to try and decide all cases of impeachment.” The Supreme Court likewise recognizes the Senate as a coequal constitutional body whose actions within its sphere are not ordinarily subject to judicial control, although grave abuse of discretion remains constitutionally significant. 

The responsibility resting on the Senate is therefore enormous.

It should explain not merely what number it chooses, but the constitutional principle producing that number.

If the denominator can change, the Senate should articulate precise, neutral criteria governing when a senator ceases to count.

If all 24 must always be counted, it should explain how that interpretation avoids rendering impeachment dysfunctional under extraordinary circumstances.

Either way, the reasoning should be written clearly enough to govern future Senates—and future accused officials—without regard to political color.

More than Sara Duterte

The framers of the Constitution deliberately made impeachment difficult. They also deliberately made it possible.

Those two principles must coexist.

Too low a threshold could transform impeachment into a parliamentary vote of no confidence, allowing temporary majorities to remove independently elected officials.

Too rigid a threshold could transform absence or incapacity into an unintended veto, making accountability impossible even after a full constitutional trial.

The challenge is to preserve both stability and accountability.

That is why the Senate should resist viewing this as simply a contest between 16 votes and some smaller number. It is defining what “two-thirds of all the Members of the Senate” will mean when constitutional theory collides with imperfect political reality.

Vice President Duterte’s fate is unquestionably important. But eventually her impeachment will become history. The rule fashioned to decide it may remain.

And years from now, when another president, vice president or constitutional officer stands before another Senate, today’s senator-judges may discover that their most enduring verdict was not whether Sara Duterte should be convicted or acquitted.

It was how the Philippine Republic decides who has the constitutional power to make that judgment. CS

Read more: Senator-judges can change 16-vote threshold to convict, say 3 former chief justices

Dr. Rafael R. Castillo is a cardiologist, educator, and public health advocate. He was president of the Philippine Heart Association (PHA) and the Asian Pacific Society of Hypertension, and was a longtime health columnist of the Inquirer. He has over 45 awards to his name, including the PHA Lifetime Achievement Award, and continues to champion preventive cardiology and public health reforms here and abroad.