The Two Thirds Rule in Japan: A Complete Guide to Constitutional Amendment Pow

Khoshnaw Rahmani, Jadetimes Staff

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 Image Source: Ryo FUKAsawa

Japan’s political system is built on a constitutional framework that has remained unchanged since 1947. For decades, debates over constitutional revision—especially Article 9—have shaped party platforms, election strategies, and coalition negotiations. Yet one procedural requirement stands at the center of every discussion: the twothirds rule in the National Diet.

When Japan’s ruling party secures a twothirds majority in the House of Representatives, it gains the institutional leverage needed to initiate constitutional amendments. This threshold does not guarantee revision, but it unlocks the legal pathway that makes amendment possible. Understanding how this rule works—and why it matters—requires examining Japan’s constitutional architecture, the political history behind it, and the strategic implications of a supermajority in the lower chamber.

1. Why the TwoThirds Rule Matters

Japan’s Constitution sets an unusually high bar for amendment. Article 96 requires:

· A twothirds majority in both houses of the Diet, and

· A national referendum, where a simple majority of valid votes must approve the change.

This means the lower house’s supermajority is only the first step, but it is the most politically consequential one. Without it, constitutional revision cannot even be proposed.

A ruling party with twothirds control of the House of Representatives gains:

· Agendasetting power to introduce amendment drafts

· Committee control to shape deliberations

· Negotiating leverage over coalition partners and opposition blocs

· The ability to pass amendment bills even if the upper house is divided

In short, the twothirds rule transforms constitutional reform from a theoretical aspiration into a legislative possibility.

2. The Constitutional Architecture Behind the Rule

Japan’s Constitution was designed to prevent unilateral changes by any single political force. The framers embedded multiple safeguards:

High parliamentary threshold

Requiring twothirds in both houses ensures broad political consensus.

Public referendum

Even if the Diet approves an amendment, the public must ratify it.

No emergency bypass

Unlike some constitutions, Japan’s charter does not allow emergency amendments or executivedriven changes.

Judicial neutrality

Courts do not interpret amendment proposals; they only review procedural legality.

These layers make Japan one of the most amendmentresistant democracies in the world.

3. Political History: How the TwoThirds Rule Has Shaped Japan’s Ruling Party

Postwar decades (1955–1990s): LDP dominance but constitutional caution

The Liberal Democratic Party (LDP) held nearcontinuous power and often commanded large majorities. Yet despite ideological interest in revising the constitution, the party rarely pursued amendments aggressively. Cold War geopolitics, public skepticism, and coalition dynamics discouraged bold moves.

1990s–2000s: Electoral reform and shifting coalitions

After the 1993 political realignment, the LDP returned to power but relied more heavily on coalition partners. Securing twothirds in both houses became increasingly difficult.

Abe era (2012–2020): The closest Japan came to revision

Under Prime Minister Shinzo Abe, the LDP and its coalition partners repeatedly approached or achieved twothirds majorities in both houses. Abe prioritized constitutional revision—especially clarifying the legal status of the SelfDefense Forces—but public opinion and coalition caution prevented a referendum.

Recent years: Fragmentation and renewed debate

As regional security concerns intensified, constitutional revision returned to the political agenda. The twothirds rule once again became the central metric for assessing whether reform was politically viable.

4. How a TwoThirds LowerHouse Majority Works in Practice

Step 1 — Drafting the amendment

The ruling party or a coalition committee prepares a proposal, often focusing on:

· Article 9 (selfdefense forces)

· Emergency powers

· Electoral reform

· Digital governance or rights provisions

Step 2 — Committee deliberation

With twothirds control, the ruling party dominates:

· Constitutional Review Committees

· Legislative committees

· Agendasetting bodies

This allows the majority to schedule debates, shape language, and move proposals forward.

Step 3 — Lowerhouse vote

A twothirds majority ensures passage even if the opposition votes as a bloc.

Step 4 — Upperhouse negotiations

The upper house may be more fragmented. A strong lowerhouse mandate increases pressure on upperhouse members to cooperate or negotiate amendments.

Step 5 — National referendum

If both houses approve, the proposal goes to the public. Japan has never held a constitutional referendum, so political parties must prepare:

· Public education campaigns

· Legal frameworks for referendum oversight

· Messaging strategies to build support

5. Political Implications of a TwoThirds Majority

1. Strengthened executive leadership

A prime minister with a supermajority gains greater authority over:

· Cabinet priorities

· Bureaucratic coordination

· Coalition bargaining

2. Opposition recalibration

Opposition parties must decide whether to:

· Cooperate on limited amendments

· Form antirevision coalitions

· Focus on public campaigning ahead of a referendum

3. Coalition dynamics

Coalition partners may support or restrain constitutional initiatives depending on their voter base and ideological stance.

4. Public opinion becomes decisive

Even with a supermajority, no amendment can pass without public approval. Polling, media narratives, and civilsociety mobilization become central political battlegrounds.

6. Comparisons with Other Constitutional Systems

United States

Amendments require twothirds of Congress and threequarters of states—similar in difficulty to Japan’s process.

Germany

Basic Law amendments require twothirds of both houses but no referendum.

South Korea

Requires twothirds of the National Assembly and a public referendum.

Japan’s system is among the most stringent, particularly because it combines a supermajority requirement with a mandatory referendum.

7. Historical Attempts at Constitutional Revision

Period	Political Context	Outcome
1950s–1970s	LDP dominance	No serious attempts due to public opposition
1990s	Political realignment	Fragmentation prevented consensus
2005–2007	LDP–Komeito coalition	Draft proposals circulated but stalled
2012–2020	Abe administration	Came closest but lacked referendum momentum
2020s	Renewed debate	Security concerns revived interest

8. Timeline: Key Moments in Japan’s Constitutional Amendment Debate

Year	Event	Significance
1947	Constitution enacted	Establishes Article 9 and amendment rules
1955	LDP founded	Begins decades of conservative dominance
2000s	First modern amendment drafts	Signals renewed interest in revision
2012–2020	Abe era	Twothirds majorities achieved but no referendum
2020s	Rising regional tensions	Constitutional debate intensifies

9. Why the TwoThirds Rule Will Continue to Shape Japanese Politics

The twothirds requirement ensures that constitutional change cannot be driven by a single election cycle or a narrow partisan coalition. It forces political actors to build broad consensus, negotiate across party lines, and engage the public directly.

From a political perspective, the rule:

· Elevates the strategic importance of LowerHouse elections

· Shapes coalition formation and party platforms

· Influences leadership contests within the ruling party

· Determines whether constitutional reform is even on the table

As long as the rule remains in place, Japan’s constitutional future will depend not only on electoral victories but on the ability of political leaders to persuade both parliament and the public.