Causation in Criminal Law: California’s Rules Explained
Causation in criminal law asks a deceptively simple question: did the defendant’s act actually cause the prohibited result? On the California Bar Exam, causation issues usually aren’t subtle — the facts telegraph them — but students still lose points by mishandling the two-step test or manufacturing a causation problem where none exists.
Get comfortable separating actual cause from proximate cause, and you’ll handle even the trickiest intervening-cause hypo cleanly. This is especially important in homicide questions, where causation frequently decides whether a defendant faces murder or a lesser charge.
What Is Causation in Criminal Law?
Criminal causation requires that a defendant’s act be both the actual cause (the “but-for” cause) and the proximate cause (a natural and probable consequence) of the prohibited result. Responsibility is cut off only when an unforeseeable, independent intervening cause breaks the chain between the defendant’s conduct and the resulting harm.
Actual Cause vs. Proximate Cause
| Test | Question Asked | Example Trap |
|---|---|---|
| Actual (but-for) cause | Would the result have occurred but for the defendant’s act? | Two shooters, each independently fatal — courts use the substantial-factor test instead |
| Proximate cause | Was the result a natural and probable consequence of the act? | An unforeseeable, independent event may sever liability even where but-for cause is clear |
Where two independently sufficient causes combine — say, two people simultaneously shoot the same victim — courts substitute a substantial-factor test for the ordinary but-for inquiry, since a strict but-for analysis would let both defendants escape liability by pointing at each other.
Foreseeable vs. Unforeseeable Intervening Causes
The chain of proximate causation breaks only for unforeseeable, independent intervening causes — not for every subsequent event. Foreseeable intervening causes do not break the chain:
- Negligent (but not grossly negligent) medical treatment
- A preexisting condition of the victim
- A reasonable response by the victim to the peril the defendant created
Unforeseeable, independent intervening causes can break the chain:
- Grossly negligent medical malpractice
- An act of God or pure coincidence
- A deliberate, independent act of a third party unconnected to the defendant’s conduct
The Eggshell-Victim Rule
The defendant takes the victim as he finds her. A hidden vulnerability — a bleeding disorder, a weak heart, a thin skull — does not excuse the defendant from liability for the resulting harm, even if a healthier victim would have survived the same conduct. Regina v. Blaue (Eng. 1975) illustrates the point starkly: a victim’s religiously motivated refusal of a blood transfusion did not break the causal chain between the defendant’s stabbing and her resulting death.
The Acceleration Rule
Where the defendant’s unlawful act combines with another cause to bring about death, the act remains the actual cause because it accelerated the death. A defendant who poisons a terminally ill victim, advancing death by even a few months, is still guilty of homicide — he caused the death by accelerating it, even though death was otherwise inevitable.
California and the Year-and-a-Day Rule: Penal Code § 194
At common law, a victim had to die within a year and a day of the defendant’s injurious act for a homicide conviction to stand, no matter how clearly the act was the but-for cause of a later death. Most modern jurisdictions have abolished this rigid rule, and California Penal Code § 194 reflects that shift: California no longer applies a strict year-and-a-day bar, though a killing occurring more than three years after the underlying act carries a rebuttable presumption that the act did not cause the death, which the prosecution must overcome with the usual proof of causation.
Worked Example
Dan shoots Vic, inflicting a wound that would be fatal within hours without treatment. Vic is rushed to the hospital and receives competent care, but dies two days later when an unrelated fire breaks out in the hospital and Vic, already weakened, cannot escape in time.
Analysis: Dan’s shooting is the actual (but-for) cause of Vic’s death — without it, Vic never would have been hospitalized and vulnerable. The closer question is proximate cause: an independent, unforeseeable hospital fire unrelated to Vic’s treatment could be a superseding event that breaks the chain of proximate causation, cutting off Dan’s liability for the death itself, though he remains liable for the underlying assault or attempted murder. Had Vic instead died from ordinary complications of the gunshot wound, or even from negligent (not grossly negligent) medical treatment, that foreseeable intervening cause would not break the chain, and Dan would face full homicide liability.
Common Mistakes to Avoid
- Conflating actual cause and proximate cause. Actual cause is a factual, mechanical inquiry; proximate cause is a policy-based, foreseeability inquiry. A defendant can satisfy one and fail the other.
- Misreading the eggshell-victim rule as a defense. It’s the opposite of a defense — it holds the defendant fully liable for the victim’s actual vulnerability, not a lesser degree of harm.
- Treating every intervening act as chain-breaking. Foreseeable intervening acts, like ordinary medical negligence, do not break causation; only unforeseeable, independent ones do.
- Manufacturing a causation issue from obvious facts. Do not spend essay space analyzing causation where the chain of events is direct and undisputed; save the analysis for a genuine intervening-cause fact pattern.
FAQ
What’s the difference between actual cause and proximate cause?
Actual cause is a factual question — would the result have occurred but for the defendant’s act? Proximate cause is a policy question — was the result a natural and probable, foreseeable consequence of that act?
Does California still follow the year-and-a-day rule?
No, not in its strict common-law form. California Penal Code § 194 has modified the rule; a death occurring more than three years after the act triggers a rebuttable presumption against causation rather than an automatic bar.
Can a defendant escape liability because a victim had a preexisting condition?
No. Under the eggshell-victim rule, the defendant takes the victim as found and remains liable for the full extent of harm, even if it resulted from a hidden vulnerability.
Key Takeaways
- Criminal causation requires both actual (but-for) cause and proximate (foreseeable, natural-and-probable) cause.
- Only unforeseeable, independent intervening causes break the chain of proximate causation; foreseeable ones do not.
- The eggshell-victim rule holds a defendant fully liable for a victim’s hidden vulnerabilities.
- California Penal Code § 194 replaced the rigid year-and-a-day rule with a rebuttable three-year presumption.
- Causation is a required element the prosecution must prove beyond a reasonable doubt — if it fails, the homicide charge fails even if intent and act are proven.
This article is educational and is not legal advice. Consult a licensed California attorney about your situation.
Related guides
- Actus Reus Explained: The Voluntary Act Rule in CA
- First-Degree Murder: California Penal Code § 189 Guide
- Second-Degree Murder: California Penal Code § 187 Rules
- Murder and Manslaughter in California