The substantial factor test is often used in criminal law and torts to assess whether the defendant’s acts or omissions were a substantial factor in causing the harm, especially when there are multiple causes. In criminal law, the substantial factor test is used to es…
substantial factor test — Definition and meaning
In criminal law, the substantial factor test is used to establish whether a defendant’s acts or omissions led to the result of the crime. The prosecution must prove that the defendant’s conduct was a substantial factor in bringing about the result. It does not need to be the sole or primary cause, but it must be more than trivial or insignificant, thus a “significant” factor. For example, if A and B independently and fatally shot C, leading to C’s death, both A and B’s actions could be considered a substantial factor in C’s death because both shots significantly contributed to the outcome.
Because the but-for test requires a much stricter proof of causation, the substantial factor test is often applied in some jurisdictions when the but-for test is too restrictive. For example, A and B would not be found for C’s death because the harm would have occurred even if either A or B did not shoot C. One way to still apply the but-for test without resorting to the substantial factor test is to elaborate the “but-for condition”: but for A or B’s voluntary act of shooting C, would C have died at the time and in the way C died?
The substantial factor test is also different from the proximate cause test in that the former focuses more on the defendant’s contribution to the harm while the latter focuses more on the foreseeability of the harm.
See: CALCRIM No. 620. Causation: Special Issues - Judicial Council of California Criminal Jury Instructions (2024 edition); People v. Pike (1988)
See: Mavroudis v. Pittsburgh-Corning Corp. (1997); Roemmich v. 3M Co. (2022); Washington Pattern Jury Instructions--Civil: WPI 15.02 Proximate Cause - Substantial Factor Test and CACI No. 430. Causation: Substantial Factor - Judicial Council of California Civil Jury Instructions (2024 edition).
The importance of substantial factor test
substantial factor test appears in U.S. legal practice across multiple practice areas. Knowing what it means — and when it applies — can determine the outcome of motions, filings, and negotiations. For non-lawyers, the value of looking up a precise definition is that legal terms often carry meanings that differ from everyday usage; relying on the common meaning can lead to costly missteps.
How substantial factor test is applied
In practice, substantial factor test is invoked when parties, judges, or attorneys need to identify the legal status of an issue, the rights of those involved, or the procedural step required next. The definition shown above is sourced from Cornell LII Wex , which is widely cited in U.S. legal practice. Because U.S. law is jurisdictionally layered — federal, state, and sometimes local — the precise application of the term can vary by court, so check the controlling authority for your specific case.