Why is the "Soshōbutsu" (Subject Matter of Litigation) Theory So Crucial for Japanese Lawsuits and Res Judicata?

Japanese Attorney at Law - Bengoshi L.L.

• 9 min read

When embarking on civil litigation in any jurisdiction, one of the most fundamental questions is: what exactly is the lawsuit about? In Japanese civil procedure, this "what"—the core legal claim or right for which a judicial decision is sought—is known as the soshōbutsu (訴訟物), often translated as the "subject matter of litigation" or "claim for relief." While it might sound like a purely academic term, the theory and practical application of soshōbutsu have profound and far-reaching consequences for how lawsuits are framed, adjudicated, and ultimately, the binding effect (res judicata) of judgments.

This article delves into the concept of soshōbutsu, explores the main theories surrounding its identification, and explains why understanding this doctrine is absolutely critical for navigating civil disputes in Japan, particularly concerning the scope of res judicata and other procedural mainstays.

A. What is Soshōbutsu?

The soshōbutsu is the specific legal right, legal relationship, or entitlement that the plaintiff asks the court to affirm or enforce through its judgment. It is, in essence, the plaintiff's concrete demand for a judicial ruling. The soshōbutsu is identified and delineated primarily by carefully examining the plaintiff's statements in their complaint (訴状 - sojō), specifically:

  • The "Gist of Claim" (請求の趣旨 - seikyū no shushi): This part of the complaint specifies the precise remedy or relief sought from the court (e.g., "The defendant shall pay the plaintiff JPY X," or "The court shall confirm that the plaintiff is the owner of Blackacre").
  • The "Cause of Action" (請求の原因 - seikyū no gen'in): This section sets out the factual allegations and the legal grounds that the plaintiff claims entitle them to the relief specified in the gist of claim.

The court's task is to adjudicate the existence or non-existence of the soshōbutsu as defined by the plaintiff.

B. Key Functions of Soshōbutsu

The concept of soshōbutsu serves several vital procedural functions:

  1. Defining the Scope of Adjudication: It determines the precise boundaries of what the court is called upon to decide. The court’s judgment must address the soshōbutsu presented.
  2. Determining the Objective Scope of Res Judicata (Kihanki-ryoku): This is arguably its most critical function. Article 114, Paragraph 1 of the Code of Civil Procedure (CCP) (民事訴訟法 - Minji Soshō Hō) states that a final and binding judgment has preclusive effect (res judicata) only with respect to "the conclusion of a judicial decision on the claim contained in the main text of the judgment." This "claim" is the soshōbutsu. Thus, how broadly or narrowly the soshōbutsu is defined dictates the scope of what is barred from re-litigation.
  3. Preventing Double Jeopardy (Jūfuku Kiso no Kinshi): CCP Article 142 prohibits a party from filing a new action when an action concerning the "same case" is already pending before a court (lis pendens). The "same case" is determined primarily by the identity of the parties and, crucially, the identity of the soshōbutsu.
  4. Guiding Claim Amendments (Uttae no Henkō): A plaintiff may amend their claim under CCP Article 143, but generally only if, among other conditions, the "basis of the claim" (請求の基礎 - seikyū no kiso) remains identical. The understanding of soshōbutsu influences the interpretation of what constitutes an identical "basis of the claim."
  5. Unit for Joinder of Claims (Seikyū no Heigō): Multiple soshōbutsu (claims) can be joined in a single lawsuit under CCP Article 136, provided certain conditions are met. The soshōbutsu serves as the individual unit for such joinder.

II. The Great Debate: Theories of Soshōbutsu

How the soshōbutsu is identified and individualized is the subject of a long-standing and significant theoretical debate in Japanese civil procedure scholarship, broadly categorized into the "traditional" (or "old") theory and various "newer" theories.

A. The Traditional Substantive Law Theory (旧訴訟物理論 - Kyū Soshōbutsu Riron / 旧実体法説 - Kyū Jittaihō Setsu)

  • Core Idea: This theory identifies the soshōbutsu with the specific substantive legal right that the plaintiff asserts and seeks to have recognized or enforced. Each distinct substantive right under civil law (e.g., a right arising from a specific contract, a right arising from a specific tort, an ownership right) constitutes a separate soshōbutsu.
  • Implication: If a plaintiff has multiple distinct legal rights, even if they arise from the same factual background or incident, each right forms a separate soshōbutsu. For instance:
    • A claim for payment based on a loan agreement is one soshōbutsu.
    • A claim for damages due to the defendant's fraudulent inducement to enter that same loan agreement (a tort claim) would be a different soshōbutsu.
    • A claim for return of a leased property based on termination of the lease contract is one soshōbutsu; a claim for its return based on the plaintiff's underlying ownership right would be another.
  • Dominant View: The traditional substantive law theory has historically been, and largely continues to be, the dominant view adopted by Japanese courts, including the Supreme Court, and supported by many legal scholars.

B. The Newer Procedural Law Theories (新訴訟物理論 - Shin Soshōbutsu Riron / 訴訟法説 - Soshōhō Setsu)

Driven by aims such as achieving more comprehensive and final dispute resolution in a single proceeding and preventing piecemeal litigation, various "newer" theories have emerged. These theories tend to define the soshōbutsu more broadly, often from a procedural or dispute-resolution perspective rather than a strictly substantive law one. Key variants include:

  1. Single Dispute Resolution Theory (一回的紛争解決説 - Ikkaiteki Funsō Kaiketsu Setsu): This approach argues that all legal claims or grounds for relief arising from a single, socially identifiable dispute or factual incident should be treated as constituting a single, comprehensive soshōbutsu. For example, all damages stemming from a single traffic accident (property damage, medical expenses, lost income, pain and suffering) would form one indivisible soshōbutsu, regardless of the different legal interests infringed.
  2. Two-Pronged Theory (二分肢説 - Nibunshi-setsu): This theory identifies the soshōbutsu based on the combination of two elements: (1) the specific relief sought by the plaintiff (the "gist of claim") and (2) the essential factual basis or "cause of action" presented. If either of these elements differs significantly, it would constitute a different soshōbutsu. This can sometimes lead to a broader or narrower conception than the traditional theory, depending on how "factual basis" is defined.

Impact of Newer Theories: Generally, these newer theories would result in a broader definition of the soshōbutsu. Consequently, a judgment would have a wider preclusive (res judicata) effect, compelling parties to bring all related claims from a single dispute in one lawsuit or risk losing them.

C. The Prevailing Stance in Practice

Despite academic debate, Japanese courts have largely maintained their adherence to the traditional substantive law theory. This has significant practical ramifications. It means that the preclusive effect of judgments (res judicata) is often narrower than it might be under, for example, the "transaction or occurrence" test used for claim preclusion in U.S. federal courts. A plaintiff might sue on one substantive legal ground and, if unsuccessful, potentially bring a subsequent lawsuit against the same defendant based on a different substantive legal ground arising from the same factual incident, because the soshōbutsu (the specific legal right asserted) would be considered different in each case.

However, it's worth noting that in certain specific types of litigation, such as disputes over rent adjustments (e.g., Supreme Court, April 26, 1973, Minshū Vol. 27, No. 3, Page 506, concerning the soshōbutsu in a claim for an increase/decrease in rent) or cases involving ongoing relationships, court interpretations sometimes lean towards ensuring a more definitive resolution that takes broader aspects of the dispute into account, even while formally adhering to the traditional theory.

III. Why Soshōbutsu Matters Profoundly: Practical Consequences

The theoretical underpinnings of soshōbutsu directly translate into critical practical consequences for litigants.

A. Res Judicata (Kihanki-ryoku): The Long Shadow of Soshōbutsu

As stated in CCP Article 114(1), a final judgment becomes binding (has res judicata effect) only with respect to the "claim" – the soshōbutsu – decided in the main text of the judgment.

  • Narrow Preclusion under Traditional Theory: If the soshōbutsu is defined narrowly based on a specific substantive right (e.g., a contractual claim for Item A), the res judicata effect is correspondingly narrow. This means a subsequent lawsuit asserting a different substantive right (e.g., a tort claim related to Item A, or a contractual claim for Item B under the same master agreement if treated as a separate right) might not be barred, even if all claims arise from the same overall business relationship or series of events.
  • Contrast with Broader Claim Preclusion: This can be a significant point of difference for those familiar with U.S. claim preclusion (res judicata), where the general rule is that a final judgment on the merits of an action precludes the parties from re-litigating issues that were or could have been raised in that action, encompassing all rights arising out of the same transaction or occurrence.

B. Prohibition of Double Jeopardy / Lis Pendens (Jūfuku Kiso no Kinshi)

CCP Article 142 bars a party from filing a new action when an action concerning the "same case" (同一事件 - dōitsu jiken) is already pending. The "same case" is primarily identified by the identity of the parties and the soshōbutsu. A narrow definition of soshōbutsu under the traditional theory means that what might be viewed as part of a single broader dispute in other jurisdictions could potentially be pursued as separate lawsuits with distinct soshōbutsu in Japan, either concurrently (if not deemed "identical") or successively.

C. Amendment of Claims (Uttae no Henkō)

A plaintiff can amend their claim (CCP Art. 143), but one of the key conditions is that the "basis of the claim" (seikyū no kiso) remains identical. The "basis of the claim" refers to the underlying factual circumstances and social dispute. How the soshōbutsu is conceptualized influences how courts interpret the "identity of the basis of the claim." If an amendment seeks to introduce what is considered an entirely new soshōbutsu under the traditional theory, it might be disallowed unless the shared factual underpinnings are extremely close and other conditions are met.

IV. Identifying the Soshōbutsu in Specific Cases

The identification of the soshōbutsu depends heavily on the substantive law invoked and how the plaintiff frames their "gist of claim" and "cause of action."

  • Contractual Claims: A claim for payment of a specific invoice (e.g., for goods delivered on a certain date under a specific purchase order) is typically one soshōbutsu. If there are multiple unpaid invoices under the same master agreement, each might be treated as giving rise to a separate soshōbutsu if they represent distinct performance obligations.
  • Tort Claims (不法行為 - fuhō kōi): Under the traditional theory, if a single negligent act causes both personal injury and property damage, the claim for personal injury damages (infringement of bodily integrity) and the claim for property damages (infringement of property rights) could technically be considered separate soshōbutsu, as they relate to different legally protected interests, although they are almost always joined in a single lawsuit for practical reasons. Similarly, asserting different theories of liability (e.g., general negligence vs. a specific statutory tort) for the same injury might be viewed as involving different soshōbutsu.
  • Property Claims: A claim for the return of a specific piece of real property based on the plaintiff's ownership right (shoyūken ni motozuku henkan seikyū) is a distinct soshōbutsu from a claim for its return based on the termination of a lease agreement (chinshaku keiyaku shūryō ni motozuku henkan seikyū).

V. Strategic Considerations for Litigants

The soshōbutsu doctrine has major strategic implications:

  1. Careful Framing of the Initial Complaint: The plaintiff's initial characterization of the soshōbutsu in the complaint (through the "gist of claim" and "cause of action") is critical. It will define the scope of the current lawsuit and, more importantly, the scope of res judicata for future purposes. All potential substantive legal grounds for relief should be considered.
  2. Understanding Res Judicata Risks and Opportunities: Litigants must be acutely aware that under the prevailing traditional theory, a judgment on one narrowly defined soshōbutsu might not preclude a subsequent lawsuit based on a different soshōbutsu, even if arising from the same set of facts. This can be a double-edged sword: it might allow a "second bite at the apple" if the first claim fails, but it also means one might face multiple suits from an opponent based on different legal theories.
  3. Pleading in the Alternative (Yobiteki Seikyū): To address the narrowness of soshōbutsu under the traditional theory and to ensure all relevant legal grounds are before the court, plaintiffs in Japan often plead claims "in the alternative" (予備的請求 - yobiteki seikyū). For example, a plaintiff might primarily claim for payment based on a contract and, alternatively, if the contract claim is denied, claim for damages in tort based on the same underlying facts. This is a common and accepted practice.
  4. Comprehensive Settlement Agreements: When settling a dispute, particularly if the litigated soshōbutsu was narrow, ensure that the settlement agreement is drafted broadly enough to cover all potential claims and soshōbutsu arising from the entire underlying dispute to achieve genuine and complete finality.
  5. Anti-Suit Injunctions (Less Relevant Domestically but Conceptual): While more common in international contexts, the concept of what constitutes the "same cause of action" for anti-suit injunction purposes would also be influenced by soshōbutsu theory.

VI. Conclusion

The concept of soshōbutsu, or the subject matter of litigation, is far more than an abstract legal theory in Japanese civil procedure; it is a doctrine with profound practical consequences that shapes the entire lifecycle of a lawsuit. It dictates what the court will decide, the preclusive effect of that decision (res judicata), the permissibility of subsequent or amended claims, and overall litigation strategy.

While academic debate continues between the traditional substantive law theory and newer procedural theories, Japanese courts have largely adhered to the traditional approach, which tends to define the soshōbutsu relatively narrowly based on distinct substantive legal rights. For businesses and legal professionals, especially those accustomed to broader claim preclusion rules in other jurisdictions, a nuanced understanding of soshōbutsu is indispensable for effectively prosecuting or defending claims and for ensuring that judicial resolutions achieve the desired scope and finality in Japan.