The "Principle of Commonness of Evidence" in Multi-Party Lawsuits: How Does Evidence Submitted by One Party Affect Others?

Japanese Attorney at Law - Bengoshi L.L.

• 7 min read

Multi-party lawsuits, where several plaintiffs or defendants are grouped into a single proceeding, present unique challenges for managing evidence. A crucial question arises: if one party submits a piece of evidence, can that evidence be considered by the court when assessing the claims or defenses of the other parties involved, even those who didn't submit it? In Japanese civil procedure, the answer is largely yes, due to the "Principle of Commonness of Evidence" (証拠共通の原則 - shōko kyōtsū no gensoku).

This principle significantly impacts how evidence operates in co-litigation (kyōdō soshō) and serves as a vital modification to the general rule of co-litigant independence. This article explores the definition, rationale, scope, and practical effects of this important doctrine.

I. Understanding Multi-Party Lawsuits (Kyōdō Soshō) in Japan: A Brief Recap

Before delving into the specifics of evidence handling, it's helpful to recall the two main types of multi-party lawsuits (joinder of parties) in Japan:

  1. Ordinary Joinder (Tsūjō Kyōdō Soshō - CCP Art. 38): Multiple plaintiffs or defendants are joined because their rights/obligations are common or arise from the same factual and legal cause. The default rule here is the Principle of Independence of Co-Litigants (共同訴訟人独立の原則 - kyōdō soshōnin dokuritsu no gensoku - CCP Art. 41), meaning procedural acts by one co-litigant generally do not affect others.
  2. Necessary Joinder (Hitsuyō-teki Kyōdō Soshō - CCP Art. 40): All indispensable parties must be joined because a judgment needs to be uniformly binding on all of them. The independence principle is largely displaced here.

The Principle of Commonness of Evidence plays a particularly interesting role in the context of ordinary joinder, by creating a shared evidentiary pool despite the general independence of the parties.

II. The Principle of Commonness of Evidence (Shōko Kyōtsū no Gensoku): Definition and Rationale

A. Core Concept

The Principle of Commonness of Evidence dictates that in a multi-party lawsuit (both ordinary and necessary joinder), any piece of evidence properly submitted into the court record by one co-litigant becomes available for consideration by the court when evaluating the factual assertions and legal positions of all other co-litigants involved in that same proceeding. This is true regardless of who initially tendered the evidence, and the evidence can be used to the benefit or detriment of any party.

As insightful legal commentaries from Japan suggest, one facet of this principle is that "evidentiary materials act for the benefit or detriment of the party who submitted the motion (for examination of evidence), i.e., evidentiary materials are not only used in favor of the party who submitted the motion." Furthermore, "the evidentiary basis (the facts to be proven by the evidence) for evidentiary materials is not limited to only the asserted facts of the party who submitted the motion." (This reflects the nuance found in the PDF snippet from Part 5, Page 1).

B. Rationale

Several rationales underpin this principle:

  1. Judicial Economy: It prevents the redundant submission of the same evidence by multiple parties. If one co-plaintiff submits a crucial document, other co-plaintiffs (or even co-defendants, if it aids their case) do not need to formally re-submit it.
  2. Truth Discovery: By allowing the court to consider all properly adduced evidence in relation to all parties, it enhances the court's ability to ascertain the substantive truth of the overall dispute.
  3. Consistency of Factual Findings: It promotes consistent factual findings across related claims being tried together, reducing the risk of contradictory conclusions within the same judgment.
  4. Modification of the Independence Principle: In ordinary joinder, where co-litigants are generally independent, shōko kyōtsū creates a crucial link by unifying the evidentiary record available for the court's assessment of each party's case.

III. Scope of Application

The Principle of Commonness of Evidence generally applies across different forms of multi-party litigation:

  • Ordinary Joinder (Tsūjō Kyōdō Soshō): This is where the principle has its most pronounced effect as a modifier of the default rule of co-litigant independence. Evidence submitted by one independent co-litigant is nonetheless available for the court to consider in relation to all others.
  • Necessary Joinder (Hitsuyō-teki Kyōdō Soshō): The principle applies with even greater force in necessary joinder. Given the requirement for a single, uniformly binding judgment (gōitsu kakutei) for all necessary co-litigants, it is inherent that all evidence submitted by any party will be considered in relation to the entire, indivisible case.
  • Auxiliary Intervention (Hojo Sanka): When an auxiliary intervenor (who joins to support one of the main parties) submits evidence, that evidence also typically becomes part of the common record. It can be used to support the assisted party's case and may also be considered by the court in relation to other parties, subject to the specific limitations on an auxiliary intervenor's actions.

IV. How the Principle Works in Practice: Effects on Co-Litigants

The application of shōko kyōtsū no gensoku has several practical consequences:

A. Use for Favorable Fact-Finding

A co-litigant (Party A) can benefit from evidence submitted by another co-litigant (Party B), even if Party B is on the opposing side or is another co-plaintiff/co-defendant with whom Party A has not explicitly coordinated. If Party B submits a document or elicits witness testimony that happens to support Party A's factual allegations, Party A's counsel can refer to that evidence in their arguments, and the court can rely on it to find facts favorable to Party A, without Party A needing to have formally tendered that specific piece of evidence themselves.

B. Use for Unfavorable Fact-Finding

Conversely, evidence submitted by one co-litigant (Party A) can be used by the court to make factual findings that are unfavorable to another co-litigant (Party B). This is true even if Party A and Party B are on the same "side" of the litigation (e.g., both are co-plaintiffs) but their specific interests or versions of events diverge on certain points. Party B cannot simply ignore evidence submitted by Party A if it is relevant to Party B's position.

C. "Evidentiary Basis" (Shōko Gen'in) Not Limited to Submitting Party's Claims

This aspect, highlighted in Japanese legal commentary, is crucial. The scope of facts that a particular piece of evidence can be used to prove (its "evidentiary basis" or shōko gen'in) is not restricted to only those specific factual allegations made by the party who originally submitted that evidence.

  • Once a document or testimony is properly in the record, the court can assess its relevance and probative value concerning any of the material facts pleaded by any of the parties in the multi-party suit.
  • For example, if co-plaintiff A submits a contract to prove point X, but a clause in that same contract is also highly relevant to proving point Y (alleged by co-plaintiff B, or even a defense point by defendant C), the court can use the contract for assessing point Y as well.

D. Restrictions on Withdrawal of Evidence

Because evidence submitted by one party becomes common to all, the ability of the submitting party to unilaterally withdraw that evidence at a later stage may be restricted. If other co-litigants have an interest in relying on that evidence (or if the court deems it important for resolving the overall dispute), the original submitting party might not be permitted to simply remove it from the record.

V. Relationship with Other Key Procedural Principles

The Principle of Commonness of Evidence interacts closely with other foundational principles of Japanese civil procedure:

  1. Principle of Independence of Co-Litigants (CCP Art. 41): As mentioned, shōko kyōtsū is a significant tempering force on this principle in ordinary joinder. While parties may file separate pleadings, make independent arguments, and even pursue different legal theories, they are generally bound by and can benefit from a common pool of admitted evidence.
  2. Principle of Commonality of Allegations (Shuchō Kyōtsū no Gensoku): This is a distinct but related principle. It generally means that a factual allegation (especially one that is favorable) made by one co-litigant can be taken into account by the court for other co-litigants on the same side, even if they haven't explicitly made the same allegation. Shōko kyōtsū deals with the evidentiary materials themselves, while shuchō kyōtsū deals with the pleaded facts. They often operate in tandem to create a more unified basis for judgment in multi-party suits.
  3. Principle of Free Evaluation of Evidence (Jiyū-Shinshō-Shugi - CCP Art. 247): The court applies its free and rational judgment to all evidence made common to the record through this principle. Shōko kyōtsū expands the universe of evidence that is subject to the judge's holistic evaluation when considering each co-litigant's case.
  4. Principle of Party Presentation (Benron-Shugi): The Principle of Commonness of Evidence operates on the evidence that has been actually submitted by the parties (or examined pursuant to a party's request). It does not grant the court the power to seek out additional evidence ex officio beyond the established procedural rules (such as specific provisions for court-ordered expert examination or examination of parties). The evidence becomes "common" once a party properly introduces it into the adversarial arena.

VI. Strategic Implications for Co-Litigants

Understanding shōko kyōtsū no gensoku is vital for crafting effective litigation strategies in multi-party cases:

  1. Coordinated (or Uncoordinated) Evidence Strategy:
    • Allied Co-Litigants: Parties on the same side with aligned interests might strategically coordinate who will bear the primary responsibility for submitting certain pieces of key evidence to avoid duplication and ensure all necessary points are covered comprehensively.
    • Divergent Interests: If co-litigants on the same side have some differing interests or factual accounts, they must be aware that evidence submitted by one might inadvertently help or harm the other.
  2. Comprehensive Vigilance: Each co-litigant and their counsel must diligently monitor all evidence submitted throughout the case, not just the evidence directly concerning their own claims or defenses, or evidence submitted by their direct opponent. Any piece of evidence can potentially impact their case.
  3. Leveraging Favorable Evidence from Any Source: If any party—even an opponent or a co-party with whom one is not allied—submits evidence that is favorable to one's own position, it should be actively highlighted and incorporated into arguments to the court.
  4. Rebutting Unfavorable Evidence Regardless of its Origin: Conversely, a party must be prepared to challenge, rebut, or explain any unfavorable evidence that appears in the record, irrespective of which co-litigant originally submitted it. One cannot simply ignore damaging evidence because "it wasn't my submission."
  5. Considerations Before Joining or Being Joined: When contemplating whether to join an existing multi-party lawsuit, or when faced with a motion for joinder, the implications of the Principle of Commonness of Evidence should be a key consideration. Joining means stepping into a shared evidentiary environment.
  6. Impact on Settlement: The common evidentiary record can influence settlement dynamics, as all parties will be assessing their positions based on the totality of evidence presented.

VII. Conclusion

The Principle of Commonness of Evidence (shōko kyōtsū no gensoku) is a cornerstone of managing evidence in Japanese multi-party civil litigation. It fosters judicial economy and the pursuit of substantive truth by creating a unified evidentiary record accessible for the court's consideration in relation to all co-litigants. While it tempers the strict independence of parties in ordinary joinder, it ensures that the court can make consistent and well-informed decisions based on all relevant information properly brought before it.

For any party involved in or anticipating multi-party lawsuits in Japan, a clear understanding of this principle is essential. It shapes how evidence submitted by one can ripple through the entire proceeding, affecting the factual findings relevant to all, and underscores the need for vigilance and strategic adaptation in a shared evidentiary landscape.