The Impeachment Threshold: A Constitutional Question the Senate Must Get Right

The debate over the voting threshold in the impeachment trial of Vice President Sara Duterte is no longer merely a question of Senate procedure. It has become a serious constitutional issue that could establish a precedent for every impeachment proceeding that follows. At the center of the controversy is one phrase in the 1987 Constitution: “two-thirds of all the Members of the Senate.”

Article XI, Section 3(6) provides that the Senate has the sole power to try and decide impeachment cases and that no person may be convicted without the concurrence of two-thirds of all Senate members. With a 24-member Senate, the traditional reading produces a threshold of 16 votes.

The current debate concerns whether that threshold should remain fixed or whether the denominator should instead be based on senators who are legally and physically qualified to participate or, as the proposed approach from the Senate majority would suggest, those actually present for the vote. This distinction may appear technical. It is not. It determines the constitutional standard by which an elected official can be removed from office.

The Case for a Fixed Threshold

There is a strong textual argument for maintaining the 16-vote threshold.

The Constitution does not say “two-thirds of the Senators present.” It specifically says “two-thirds of all the Members of the Senate.” The Senate's own impeachment rules similarly state that an article must be sustained by two-thirds of all the Members.

Retired Supreme Court Associate Justice Adolfo Azcuna has taken this position, arguing that “all” refers to Senate membership itself, rather than the number of senators who happen to be present or capable of participating when judgment is rendered. Under this interpretation, the denominator remains 24 as long as there are 24 sitting senators. This interpretation has an important institutional rationale.

Impeachment is not an ordinary legislative vote. It is a constitutional mechanism for removing some of the highest officials of the Republic. The requirement of a two-thirds vote is therefore intended to demand a broad level of agreement before removal can occur.

A fixed threshold provides certainty.

Everyone knows before the final vote that 16 votes are necessary. The required number does not rise or fall depending on attendance, absence, suspension, or other circumstances.

The Argument for Counting Qualified or Participating Senators

There is, however, another serious constitutional interpretation. Former Chief Justice Hilario Davide Jr. has argued that the denominator should consist of senators who are legally and physically qualified to participate in the proceedings rather than automatically including all 24 members. This argument focuses on a practical constitutional problem: should a senator who is legally incapable of participating in the impeachment trial effectively count as a vote against conviction by remaining in the denominator?

This interpretation does not necessarily seek to weaken the two-thirds requirement. Instead, it treats two-thirds as a proportion that should be calculated against the actual body capable of rendering the judgment.

That is a legitimate constitutional question. But it is different from simply saying that attendance should determine the threshold.

Why “Senators Present” Is More Controversial

This is where the proposal to base the threshold on senators present deserves particularly careful scrutiny.

There is an important difference between:

all members of the Senate;

members legally qualified to participate; and

members physically present during the vote.

These concepts should not automatically be treated as interchangeable.

If the threshold becomes dependent simply on attendance, the constitutional requirement could potentially change according to who is in the chamber at the decisive moment.

For example, if all 24 senators are counted, two-thirds requires 16 votes. If only 21 senators are included, two-thirds becomes 14. If 18 are included, it becomes 12. The mathematical formula remains two-thirds, but the constitutional protection becomes progressively different. That is why the Senate must be extremely precise about what it means by “members” and what circumstances justify excluding a senator from the denominator.

The Constitution Should Not Be Interpreted According to the Immediate Political Circumstances

The greatest concern is not necessarily that one interpretation produces a higher threshold and another produces a lower one. The deeper concern is precedent. The Senate should not establish a constitutional interpretation merely because it produces a more convenient result in the impeachment case currently before it.

The decision made today could become the rule invoked in a future impeachment involving a president, vice president, Supreme Court justice, Constitutional Commission member, or Ombudsman. That future case may involve completely different political alliances. A rule that appears beneficial to one political bloc today could operate against that same bloc tomorrow.

This is precisely why constitutional rules should be interpreted from constitutional text and institutional principles rather than from the immediate political consequences of a particular case.

The 2001 Treaty Precedent Adds Another Dimension

The Senate majority has also raised a historical Senate precedent involving the approval of international treaties. In 2001, 13 senators concurred in four treaties despite Article VII, Section 21 of the Constitution also requiring the concurrence of at least two-thirds of “all the Members of the Senate.” Majority Leader Juan Miguel Zubiri has cited this episode as a question for the Senate's constitutional advisers: whether that precedent demonstrates that the phrase can operate differently from a strict 24-member denominator.

This precedent deserves examination, but it should not automatically resolve the impeachment question. A past parliamentary practice may be relevant to constitutional interpretation, but the Senate should still determine whether that practice was constitutionally correct, whether it was subsequently accepted or challenged, and whether the treaty provision and impeachment provision should be interpreted identically. Past practice is evidence to examine not necessarily a substitute for constitutional text.

The Real Question: Interpretation or Constitutional Change?

This is ultimately where the debate becomes significant. If the Constitution says two-thirds of all Senate members, and the Senate adopts a rule under which two-thirds is calculated only from those present, the Senate must explain why that interpretation does not effectively change the constitutional threshold.

There is a difference between interpreting an ambiguous constitutional provision and altering the practical effect of that provision through procedural rules. The Senate unquestionably has authority to establish rules for conducting its impeachment proceedings. Article XI also directs Congress to promulgate impeachment rules. But procedural rules cannot simply override an express constitutional requirement.

Therefore, the Senate's explanation must be more substantial than: “This is how we calculate two-thirds.”

It must answer the prior question:

Who exactly are the “Members of the Senate” referred to by the Constitution for purposes of an impeachment conviction?

A Better Approach: Define the Denominator Before the Final Vote

Whatever interpretation the Senate ultimately adopts, the most important institutional requirement should be clarity.

The Senate should establish, before the final vote:

• who is included in the denominator;

• who may legally participate;

• whether physical absence affects the denominator;

• whether suspension or other incapacity affects the denominator;

• when the denominator is fixed;

• whether it can change during the trial; and

• how fractional calculations, if applicable, are handled.

These questions should be resolved before senators cast their votes, not after the outcome becomes apparent.

That would strengthen confidence in the proceedings regardless of the eventual result.

This Is Bigger Than the Duterte Impeachment Case

The impeachment trial of Vice President Sara Duterte is undoubtedly the immediate context of this controversy. But the constitutional principle extends far beyond one person or one political administration. The Constitution is supposed to provide rules that survive changes in presidents, political parties, Senate majorities, and political alliances. That is why the Senate should resist the temptation to view the threshold question exclusively through the lens of the present political conflict.

The proper question is not: “Which threshold produces the result we want?”

It should be: “What interpretation of the Constitution can the country consistently apply even when the political circumstances are completely different?”

That is the standard a constitutional democracy should demand.

Conclusion: Protect the Constitution First

The dispute over whether impeachment conviction requires 16 votes or two-thirds of a smaller group of participating senators is not simply an argument about numbers. It is an argument about the meaning of constitutional safeguards. A fixed 16-vote requirement emphasizes the literal phrase “all the Members of the Senate.” A qualified-member approach emphasizes the ability of only legally participating senators to exercise the Senate's impeachment power. The proposal to count only those present introduces an additional question about whether attendance should influence a constitutionally prescribed supermajority.

There are serious legal arguments on more than one side, and constitutional experts have publicly disagreed on the issue. For that reason, the Senate should proceed with exceptional caution. The objective should not be to make conviction easier or more difficult. The objective should be to establish a constitutional rule that remains defensible regardless of who occupies Malacañang, who controls the Senate, and who stands accused in the next impeachment proceeding.

The credibility of the impeachment process will depend not only on the final verdict, but also on whether Filipinos can look back at the proceedings and say that the constitutional rules were applied consistently, transparently, and independently of the political circumstances of the moment.