"But-For" Causation Isn't Enough: How Does Japanese Criminal Law Establish a Causal Link Between an Act and a Result?

Japanese Attorney at Law - Bengoshi L.L.

• 10 min read

In any legal system, establishing a causal link between a defendant's act and a prohibited result is a fundamental requirement for imposing criminal liability for "result crimes" (結果犯, kekka-han)—offenses where the law punishes the causing of a specific outcome, such as death in homicide or injury in assault. While the simple "but-for" test (i.e., the result would not have occurred but for the defendant's act) serves as a basic starting point, Japanese criminal law, like many sophisticated legal systems, employs a more nuanced and refined approach to determine legal causation (因果関係, inga kankei). This article explores the evolution and current state of causation theory in Japanese criminal jurisprudence, including how intervening factors are assessed.

The Starting Line: The "Criminal Act" (Jikkō Kōi) and Its Inherent Danger

Before delving into the theories of causation, it's crucial to understand from what point the causal chain is traced. In Japanese criminal law, causation is assessed from the defendant's "criminal act" (実行行為, jikkō kōi). This is the act that fulfills the conduct element of the crime as defined in its constituent elements (kōsei yōken).

Crucially, this jikkō kōi itself must possess a "realistic danger" (現実的危険性, genjitsuteki kikensei) of bringing about the prohibited result. Acts that are merely preparatory and do not yet carry this threshold of direct danger are generally not considered the starting point for the causal analysis relevant to the completed crime. For instance, merely purchasing a weapon would not be the jikkō kōi from which causation for a subsequent homicide is traced; the act of using the weapon to attack the victim would be.

Beyond the "But-For" Test: Evolution of Causation Theories in Japan

While factual causation is a necessary prerequisite, Japanese law has long recognized its insufficiency as the sole determinant of legal causation.

1. The Conditio Sine Qua Non (条件説, Jōken Setsu) – The "But-For" Test

The Jōken Setsu, or theory of conditions, is essentially the "but-for" test. It asks: if the defendant's act had not occurred, would the prohibited result have still ensued? If the answer is no, then the act is a factual cause. This theory provides a broad initial filter, identifying all potential contributing factors.

However, the Jōken Setsu faces limitations. The traditional formula of "hypothetical elimination" (if X had not happened, Y would not have happened) can become problematic in situations involving multiple potential causes (e.g., two individuals independently inflict fatal wounds on a victim) or when trying to isolate the impact of a specific act in a complex chain of events. Despite these criticisms, it remains a foundational element of any causation inquiry.

2. The Era of Adequate Causation (相当因果関係説, Sōtō Inga Kankei Setsu)

For many years, the dominant theory in Japanese criminal law for refining factual causation was the Adequate Causation Theory (Sōtō Inga Kankei Setsu). This theory posits that for legal causation to exist, not only must the act be a conditio sine qua non of the result, but the result must also be an "adequate" or "foreseeable" consequence of the act. The aim was to exclude liability for results that were highly abnormal, extraordinary, or unforeseeable from the standpoint of ordinary human experience.

The judgment of "adequacy" involved considering various factors, and different sub-theories emerged based on the "judgment basis" (handan kitei):

  • Subjective Theory: Focused on what the specific actor knew or could have foreseen.
  • Objective Theory: Considered all circumstances existing at the time of the act, plus any objectively foreseeable subsequent events, from the standpoint of an omniscient observer.
  • Eclectic/Mixed Theory (prevailing within adequate causation): Assessed adequacy based on what an ordinary, prudent person could have foreseen at the time of the act, supplemented by any special knowledge or foresight the defendant actually possessed.

The Adequate Causation Theory essentially required that the defendant's act created a sufficient danger of the result occurring, and that this danger subsequently materialized into the actual result. It sought to limit liability by focusing on the typicality or normality of the causal progression.

The Current Mainstream: Realization of Danger (危険の現実化, Kiken no Genjitsuka)

In more recent decades, Japanese courts, including the Supreme Court, have increasingly adopted and refined the Theory of Realization of Danger (Kiken no Genjitsuka) as the primary framework for analyzing legal causation. This approach is sometimes seen as an evolution or a more concrete application of certain aspects previously embedded within the Adequate Causation Theory.

The core idea of the Kiken no Genjitsuka theory is that legal causation is established if the specific, realistic, and objective danger inherent in the defendant's criminal act (jikkō kōi) materialized or realized itself in the prohibited result.

Key aspects of this theory include:

  • Objective Assessment of Danger: The danger created by the defendant's act is assessed objectively, based on all circumstances existing at the time of the act, irrespective of the defendant's subjective foresight of the specific causal chain (though mens rea regarding the result itself is a separate inquiry).
  • Materialization of the Specific Risk: It's not enough that the act was dangerous in a general sense; the specific type of danger associated with the criminal act must be what led to the result.
  • Diminished Role of "Normality" of Causal Process: Unlike some interpretations of adequate causation that heavily emphasized the typicality or normality of the causal chain, the Kiken no Genjitsuka theory can accommodate unusual or atypical causal developments. If the initial, specific danger created by the act is the one that ultimately produces the result, causation can be affirmed even if the path from act to result was somewhat extraordinary. The "empirical normality" of the causal process is not an independent, decisive criterion but rather one factor in assessing whether the original danger realized itself.

This theory provides a more direct focus on the direct dangerousness of the criminal act itself and its fruition, rather than relying heavily on broader notions of general foreseeability of the entire causal sequence.

A crucial test for any causation theory is how it handles intervening causes—events or actions that occur after the defendant's initial act but before the final result. Under the Kiken no Genjitsuka framework, the question is whether the intervening cause broke the chain of causation by introducing a new, independent danger that was not a realization of the risk created by the defendant's act, or whether it was merely a factor through which the original danger materialized.

Japanese courts have addressed various scenarios:

A. The Victim's Pre-existing Conditions or Peculiarities (被害者の特殊事情, higaisha no tokushu jijō)

The general principle, often expressed as "taking the victim as they are found," largely holds. If the defendant's culpable act directly contributes to the prohibited result (e.g., death or injury), the fact that the victim had an unknown pre-existing vulnerability (like a medical condition) that made them more susceptible to the harm will generally not negate causation. The danger created by the defendant's act is seen as having realized itself in the harm to that particular victim.

  • The Futon-Mushi Case (Supreme Court ruling, June 17, 1971) is illustrative. The defendant assaulted the victim by pressing a futon over their face. The victim, who had a severe, unknown heart condition, died. The Court upheld causation for death, stating that even if the defendant was unaware of the victim's special condition and could not foresee the lethal result from such an assault on a healthy person, the assault combined with the pre-existing condition to cause death, and the defendant's act was a cause. The danger of the defendant’s act of suffocation realized itself in the context of the victim’s vulnerability.

B. The Victim's Own Subsequent Actions (被害者の行為の介入, higaisha no kōi no kainyū)

If the victim's own actions intervene between the defendant's act and the result, causation is maintained if the victim's conduct was a foreseeable or natural consequence of the situation created by the defendant, or if the defendant's act still contributed significantly to the result despite the victim's actions.

  • In the High-Speed Road Entry Case (Supreme Court ruling, July 16, 2003), a victim fleeing a prolonged and violent assault entered a highway in desperation and was struck and killed by a vehicle. The Court found that the victim's act of entering the highway, while inherently dangerous, was a direct result of the extreme fear induced by the defendants' assault and was not a "markedly unnatural or inappropriate" means of escape under the circumstances. Thus, the defendants' assault was held to be causally linked to the death.
  • The Night Scuba Diving Case (Supreme Court ruling, December 17, 1992) involved a scuba diving instructor whose negligent actions (e.g., leaving students unattended) created a dangerous situation. A student subsequently drowned, partly due to their own and an assistant's arguably inappropriate actions. The Court upheld causation against the instructor, finding that the subsequent improper actions were "induced" by the instructor's initial negligence and the perilous situation it created.
  • Conversely, if the victim’s intervening act is truly independent, highly abnormal, and unforeseeable, it might break the causal chain. However, as seen in the Judo Therapist Case (Supreme Court ruling, May 11, 1988), where a judo therapist gave fatally wrong medical advice which the victim followed, the victim’s "blameworthy" reliance did not negate causation because the therapist's initial act of giving dangerous advice carried an inherent risk that materialized.
  • If a victim, after being injured by the defendant, fails to follow medical advice or acts negligently regarding their own recovery, this generally does not break causation if the original injury inflicted by the defendant was itself a substantial and operating cause of the ultimate harm (e.g., death). The Supreme Court ruling of February 17, 2004, supports this. However, if the initial injury was minor and easily treatable, and the death resulted primarily from the victim's subsequent gross and unforeseeable negligence, the causal link might be severed.

C. Intervening Acts of Third Parties (第三者の行為の介入, daisan-sha no kōi no kainyū)

When a third party's actions intervene, the analysis often hinges on the foreseeability of the third party's act and whether the defendant's initial act still played a substantial role in the outcome.

  • If the defendant's act created a decisive and dangerous condition, and the third party's subsequent act (even if also culpable) merely contributes to or accelerates the result that was already risked by the defendant, causation is often upheld. In the Osaka Nankō Case (Supreme Court ruling, November 20, 1990), the defendant inflicted a life-threatening brain hemorrhage on the victim. Later, while the victim was still alive but unconscious, an unknown third party struck the victim with a piece of wood, which was found to have slightly hastened the death. The Court upheld the defendant's liability for homicide, reasoning that the initial assault had already created the fatal injury, and the third party's act did not break this causal chain.
  • However, if the third party's act is an independent, voluntary, and unforeseeable act that becomes the primary operative cause of the result, it may be deemed a superseding cause that breaks the chain of causation from the defendant's initial act. The U.S. Soldier Hit-and-Run Case (Supreme Court ruling, October 24, 1967) is a key example. The defendant driver (A) struck a cyclist, injuring him and knocking him onto the car roof. A passenger (B) in A's car, without A's direct involvement at that moment, then dragged the unconscious victim from the roof, causing him to fall onto the road and sustain fatal head injuries. The Court found that B's actions were "not ordinarily foreseeable from common experience" and broke the causal link from A's initial negligent driving to the death, particularly if the fatal injury could not be definitively attributed solely to A's initial impact.
  • Cases where a defendant's initial negligence creates a highly dangerous situation (e.g., unlawfully stopping vehicles on a highway) and a subsequent (and perhaps also negligent) act by a third party directly precipitates the harm (e.g., another vehicle colliding with the stopped cars) often find causation intact if the third party's act was a foreseeable consequence of the hazardous situation created by the defendant (Supreme Court ruling, October 19, 2004; Supreme Court ruling, March 27, 2006).

D. The Defendant's Own Subsequent Intervening Acts (行為者の行為の介入, kōisha no kōi no kainyū)

If the defendant themself performs a subsequent act that contributes to the result, the situation is analyzed based on whether the subsequent act was part of the unfolding of the original criminal plan or the realization of the danger created by the initial act.

  • In a notable Daishin-in ruling from April 30, 1923, the defendant strangled the victim and, mistakenly believing the victim to be dead, subsequently moved the body to a beach to hide it. The victim ultimately died from the combined effects of the initial strangulation and sand inhalation/exposure from being abandoned. The court upheld a conviction for homicide, effectively treating the entire sequence as a single transaction driven by the initial homicidal intent, where the initial danger realized itself through the subsequent (misguided) acts.
  • The Bear Hunter Case (Supreme Court ruling, March 22, 1978) presents a contrasting scenario. The defendant negligently shot and seriously injured the victim, mistaking him for a bear. Shortly thereafter, purportedly to end the victim's suffering (or to conceal the initial act), the defendant intentionally shot the victim again, killing him. The Supreme Court treated these as two distinct criminal events: negligent injury followed by homicide. This implies that the subsequent intentional killing was seen as a new, superseding cause of death, breaking the causal chain from the initial negligent act to the death for the purposes of a negligent homicide charge. If the initial negligent shot had already inflicted a fatal wound, the analysis might differ, focusing on whether the second intentional shot merely accelerated an inevitable death or constituted an independent cause.

Causation in a Business Context

Understanding these principles of causation is vital in the business context, particularly for:

  • Product Liability: Establishing a causal link between a product defect and a consumer's injury or damage. Intervening actions by the consumer or third parties can complicate this.
  • Environmental Offenses: Proving that a specific discharge or emission from a company's facility caused particular environmental harm or health problems, especially when multiple potential polluters exist.
  • Workplace Accidents: Determining whether a failure in safety protocols or equipment by the company (or its management) was a legal cause of an employee's injury or death, especially if the employee's own actions or those of a co-worker contributed.
  • Financial Crimes: In cases of fraud or embezzlement leading to financial loss, the causal connection between the deceptive act or breach of trust and the actual financial detriment must be clearly established.

The "realization of danger" theory, with its objective assessment of the risk created by the initial act, means that businesses cannot easily escape liability by pointing to unusual or slightly unforeseeable intervening events if their initial misconduct set a specific harmful chain of events in motion.

In conclusion, Japanese criminal law has moved beyond a simplistic "but-for" test for causation. The prevailing "realization of danger" (Kiken no Genjitsuka) theory requires a nuanced assessment of whether the specific objective danger inherent in the defendant's criminal act actually materialized into the prohibited result. This involves a careful examination of the entire causal sequence, including any intervening acts by the victim, third parties, or even the defendant themself, to determine if the original risk was the legally attributable cause of the harm. For businesses, this sophisticated approach underscores the need to consider not just the immediate consequences of their actions or inactions, but also the foreseeable chain of events that their conduct might set in motion.