CACI 430 Causation: Substantial Factor

California Civil Jury Instructions CACI

430 Causation: Substantial Factor

A substantial factor in causing harm is a factor that a reasonable person would consider to have contributed to the harm. It must be more than a remote or trivial factor. It does not have to be the only cause of the harm.

[Conduct is not a substantial factor in causing harm if the same harm would have occurred without that conduct.]

New September 2003; Revised October 2004, June 2005, December 2005, December 2007, May 2018, May 2020, November 2020

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Directions for Use

As phrased, this definition of “substantial factor” subsumes the “but for” test of causation, that is, “but for” the defendant’s conduct, the plaintiff’s harm would not have occurred. (Mitchell v. Gonzales (1991) 54 Cal.3d 1041, 1052 [1 Cal.Rptr.2d 913, 819 P.2d 872]; see Rest.2d Torts, § 431.) The optional last sentence makes this explicit, and in some cases it may be error not to give this sentence. (See Soule v. GM Corp. (1994) 8 Cal.4th 548, 572–573 [34 Cal.Rptr.2d 607, 882 P.2d 298]; Rest.2d Torts, § 432(1).)

“Conduct,” in this context, refers to the culpable acts or omissions on which a claim of legal fault is based, e.g., negligence, product defect, breach of contract, or dangerous condition of public property. This is in contrast to an event that is not a culpable act but that happens to occur in the chain of causation, e.g., that the plaintiff’s alarm clock failed to go off, causing her to be at the location of the accident at a time when she otherwise would not have been there. The reference to “conduct” may be changed as appropriate to the facts of the case.

The “but for” test of the last optional sentence does not apply to concurrent independent causes, which are multiple forces operating at the same time and independently, each of which would have been sufficient by itself to bring about the same harm. (Viner v. Sweet (2003) 30 Cal.4th 1232, 1240 [135 Cal.Rptr.2d 629, 70 P.3d 1046]; Barton v. Owen (1977) 71 Cal.App.3d 484, 503–504 [139 Cal.Rptr. 494]; see Rest.2d Torts, § 432(2).) Accordingly, do not include the last sentence in a case involving concurrent independent causes. (See also Major v. R.J. Reynolds Tobacco Co. (2017) 14 Cal.App.5th 1179, 1198 [222 Cal.Rptr.3d 563] [court did not err in refusing to give last sentence of instruction in case involving exposure to carcinogens in cigarettes].)

In cases of multiple (concurrent dependent) causes, CACI No. 431, Causation: Multiple Causes, should also be given.

A case in which the plaintiff’s claim is based on disease resulting from asbestos exposure requires a different instruction. (Rutherford v. Owens-Illinois, Inc. (1997) 16 Cal.4th 953, 977 [67 Cal.Rptr.2d 16, 941 P.2d 1203]; Lopez v. The Hillshire Brands Co. (2019) 41 Cal.App.5th 679, 688 [254 Cal.Rptr.3d 377] [citing previous discussion of issues related to asbestos cases in Directions for Use of this instruction and CACI No. 435].) Give CACI No. 435, Causation for Asbestos-Related Cancer Claims, and do not give this instruction. (But see Petitpas v. Ford Motor Co. (2017) 13 Cal.App.5th 261, 298–299 [220 Cal.Rptr.3d 185] [not error to give both CACI Nos. 430 and 435 in case with both product liability and premises liability defendants].)

Sources and Authority

“The test for joint tort liability is set forth in section 431 of the Restatement of Torts 2d, which provides: ‘The actor’s negligent conduct is a legal cause of harm to another if (a) his conduct is a substantial factor in bringing about the harm, and, (b) there is no rule of law relieving the actor from liability because of the manner in which his negligence has resulted in the harm.’ Section 431 correctly states California law as to the issue of causation in tort cases.” (Wilson v. Blue Cross of So. Cal. (1990) 222 Cal.App.3d 660, 671–672 [271 Cal.Rptr. 876].)

“California has definitively adopted the substantial factor test of the Restatement Second of Torts for cause-in-fact determinations. Under that standard, a cause in fact is something that is a substantial factor in bringing about the injury. The substantial factor standard generally produces the same results as does the ‘but for’ rule of causation which states that a defendant’s conduct is a cause of the injury if the injury would not have occurred ‘but for’ that conduct. The substantial factor standard, however, has been embraced as a clearer rule of causation—one which subsumes the ‘but for’ test while reaching beyond it to satisfactorily address other situations, such as those involving independent or concurrent causes in fact.” (Rutherford, supra, 16 Cal.4th at pp. 968–969, internal citations omitted.)

“The term ‘substantial factor’ has not been judicially defined with specificity, and indeed it has been observed that it is ‘neither possible nor desirable to reduce it to any lower terms.’ This court has suggested that a force which plays only an ‘infinitesimal’ or ‘theoretical’ part in bringing about injury, damage, or loss is not a substantial factor. Undue emphasis should not be placed on the term ‘substantial.’ For example, the substantial factor standard, formulated to aid plaintiffs as a broader rule of causality than the ‘but for’ test, has been invoked by defendants whose conduct is clearly a ‘but for’ cause of plaintiff’s injury but is nevertheless urged as an insubstantial contribution to the injury. Misused in this way, the substantial factor test ‘undermines the principles of comparative negligence, under which a party is responsible for his or her share of negligence and the harm caused thereby.’ ” (Rutherford, supra, 16 Cal.4th at pp. 968–969, internal citations omitted.)

“The substantial factor standard is a relatively broad one, requiring only that the contribution of the individual cause be more than negligible or theoretical. Thus, ‘a force which plays only an “infinitesimal” or “theoretical” part in bringing about injury, damage, or loss is not a substantial factor’, but a very minor force that does cause harm is a substantial factor. This rule honors the principle of comparative fault.” (Bockrath, supra, 21 Cal.4th at p. 79, internal citations omitted.)

“[G]iving CACI No. 430, which states that a factor is not substantial when it is ‘remote or trivial,’ could be misleading in an asbestos case, where the long latency period necessitates exposures will have been several years earlier. Jury instructions therefore should not suggest that a long latency period, in which the exposure was temporally ‘remote,’ precludes an otherwise sufficient asbestos claim. ‘ “Remote” often connotes a time limitation. Nothing in Rutherford suggests such a limitation; indeed, asbestos cases are brought long after exposure due to the long-term latent nature of asbestos-related diseases.’ It was not error for the court to give CACI No. 435 alone instead of CACI No. 430.” (Lopez, supra, 41 Cal.App.5th at p. 688, internal citation omitted.)

“The text of Restatement Torts second section 432 demonstrates how the ‘substantial factor’ test subsumes the traditional ‘but for’ test of causation. Subsection (1) of section 432 provides: ‘Except as stated in Subsection (2), the actor’s negligent conduct is not a substantial factor in bringing about harm to another if the harm would have been sustained even if the actor had not been negligent.’ … Subsection (2) states that if ‘two forces are actively operating … and each of itself is sufficient to bring about harm to another, the actor’s negligence may be found to be a substantial factor in bringing it about.’ ” (Viner, supra, 30 Cal.4th at p. 1240, original italics.)

“Because the ‘substantial factor’ test of causation subsumes the ‘but for’ test, the ‘but for’ test has been phrased in terms of ‘substantial factor,’ as follows, in the context, as here, of a combination of causes dependent on one another: A defendant’s negligent conduct may combine with another factor to cause harm; if a defendant’s negligence was a substantial factor in causing the plaintiff’s harm, then the defendant is responsible for the harm; a defendant cannot avoid responsibility just because some other person, condition, or event was also a substantial factor in causing the plaintiff’s harm; but conduct is not a substantial factor in causing harm if the same harm would have occurred without that conduct.” (Yanez v. Plummer (2013) 221 Cal.App.4th 180, 187 [164 Cal.Rptr.3d 309].)

“Giving CACI No. 430 in its entirety also would have meant instructing the jury on the principle of ‘but-for’ causation. Although generally subsumed within the substantial factor test, ‘the but-for test is inappropriate in cases when two forces are actively operating and each is sufficient to bring about the harm.’ … ‘If a plaintiff [or decedent] has developed a disease after having been exposed to multiple defendants’ asbestos products, medical science [is] unable to determine which defendant’s product included the specific fibers that caused the plaintiff’s [or decedent’s] disease.’ A ‘but-for’ instruction is therefore inappropriate in the asbestos context, at least when there are multiple sources of exposure. (Lopez, supra, 41 Cal.App.5th at p. 688, internal citations omitted.)

“That the Use Notes caution against giving the more general CACI No. 430 in a mesothelioma case, when the more specific instruction CACI No. 435 is more applicable, does not support a conclusion that it was error to give both instructions. CACI No. 430 is a correct statement of the law relating to substantial factor causation, even though, as Rutherford [v. Owens-Illinois, Inc.] noted, more specific instructions also must be given in a mesothelioma case. Because the more specific CACI No. 435 also was given, we do not find that the trial court erred by giving both instructions.” (Petitpas, supra, 13 Cal.App.5th p. 299, original italics.)

“A tort is a legal cause of injury only when it is a substantial factor in producing the injury. If the external force of a vehicle accident was so severe that it would have caused identical injuries notwithstanding an abstract ‘defect’ in the vehicle’s collision safety, the defect cannot be considered a substantial factor in bringing them about. [¶] The general causation instruction given by the trial court correctly advised that plaintiff could not recover for a design defect unless it was a ‘substantial factor’ in producing plaintiff’s ‘enhanced’ injuries. However, this instruction dealt only by ‘negative implication’ with [defendant]’s theory that any such defect was not a ‘substantial factor’ in this case because this particular accident would have broken plaintiff’s ankles in any event. As we have seen, [defendant] presented substantial evidence to that effect. [Defendant] was therefore entitled to its special instruction, and the trial court’s refusal to give it was error.” (Soule, supra, 8 Cal.4th at p. 572–573, original italics, footnote and internal citations omitted.)

“The first element of legal cause is cause in fact … . The ‘but for’ rule has traditionally been applied to determine cause in fact. The Restatement formula uses the term substantial factor ‘to denote the fact that the defendant’s conduct has such an effect in producing the harm as to lead reasonable men to regard it as a cause.’ ” (Mayes v. Bryan (2006) 139 Cal.App.4th 1075, 1095 [44 Cal.Rptr.3d 14], internal citations omitted.)

“If the accident would have happened anyway, whether the defendant was negligent or not, then his or her negligence was not a cause in fact, and of course cannot be the legal or responsible cause.” (Toste v. CalPortland Construction (2016) 245 Cal.App.4th 362, 370 [199 Cal.Rptr.3d 522].)

“We have recognized that proximate cause has two aspects. ‘ “One is cause in fact. An act is a cause in fact if it is a necessary antecedent of an event.” ’ This is sometimes referred to as ‘but-for’ causation. In cases where concurrent independent causes contribute to an injury, we apply the ‘substantial factor’ test of the Restatement Second of Torts, section 423, which subsumes traditional ‘but for’ causation. This case does not involve concurrent independent causes, so the ‘but for’ test governs questions of factual causation.” (State Dept. of State Hospitals v. Superior Court (2015) 61 Cal.4th 339, 354 [188 Cal.Rptr.3d 309, 349 P.3d 1013], original italics, footnote omitted.)

“The second aspect of proximate cause ‘focuses on public policy considerations. Because the purported [factual] causes of an event may be traced back to the dawn of humanity, the law has imposed additional “limitations on liability other than simple causality.” [Citation.] “These additional limitations are related not only to the degree of connection between the conduct and the injury, but also with public policy.” [Citation.] Thus, “proximate cause ‘is ordinarily concerned, not with the fact of causation, but with the various considerations of policy that limit an actor’s responsibility for the consequences of his conduct.’ ” [Citation.]’ ” (State Dept. of State Hospitals, supra, 61 Cal.4th at p. 353, internal citation omitted.)

“On the issue … of causation, as on other issues essential to the cause of action for negligence, the plaintiff, in general, has the burden of proof. The plaintiff must introduce evidence which affords a reasonable basis for the conclusion that it is more likely than not that the conduct of the defendant was a cause in fact of the result. A mere possibility of such causation is not enough; and when the matter remains one of pure speculation or conjecture, or the probabilities are at best evenly balanced, it becomes the duty of the court to direct a verdict for the defendant.” (Leyva v. Garcia (2018) 20 Cal.App.5th 1095, 1104 [236 Cal.Rptr.3d 128].)

“ ‘Whether a defendant’s conduct actually caused an injury is a question of fact … that is ordinarily for the jury … .’ ‘[C]ausation in fact is ultimately a matter of probability and common sense: “[A plaintiff] is not required to eliminate entirely all possibility that the defendant’s conduct was not a cause. It is enough that he introduces evidence from which reasonable [persons] may conclude that it is more probable that the event was caused by the defendant than that it was not. The fact of causation is incapable of mathematical proof, since no [person] can say with absolute certainty what would have occurred if the defendant had acted otherwise. If, as a matter of ordinary experience, a particular act or omission might be expected to produce a particular result, and if that result has in fact followed, the conclusion may be justified that the causal relation exists. In drawing that conclusion, the triers of fact are permitted to draw upon ordinary human experience as to the probabilities of the case.” ’ … ‘ “A mere possibility of … causation is not enough; and when the matter remains one of pure speculation or conjecture, or the probabilities are at best evenly balanced, it becomes the duty of the court to direct a verdict for the defendant.” ’ ” (Raven H. v. Gamette (2007) 157 Cal.App.4th 1017, 1029–1030 [68 Cal.Rptr.3d 897], internal citations omitted.)

“Ordinarily, proximate cause is a question of fact which cannot be decided as a matter of law from the allegations of a complaint. … Nevertheless, where the facts are such that the only reasonable conclusion is an absence of causation, the question is one of law, not of fact.” (Modisette v. Apple Inc. (2018) 30 Cal.App.5th 136, 152 [241 Cal.Rptr.3d 209].)

“[E]vidence of causation ‘must rise to the level of a reasonable probability based upon competent testimony. [Citations.] “A possible cause only becomes ‘probable’ when, in the absence of other reasonable causal explanations, it becomes more likely than not that the injury was a result of its action.” [Citation.] The defendant’s conduct is not the cause in fact of harm “ ‘where the evidence indicates that there is less than a probability, i.e., a 50-50 possibility or a mere chance,’ ” that the harm would have ensued.’ ” (Bowman v. Wyatt (2010) 186 Cal.App.4th 286, 312 [111 Cal.Rptr.3d 787].)

“However the test is phrased, causation in fact is ultimately a matter of probability and common sense.” (Osborn v. Irwin Memorial Blood Bank (1992) 5 Cal.App.4th 234, 253 [7 Cal.Rptr.2d 101], relying on Rest.2d Torts, § 433B, com. b.)

“As a general matter, juries may decide issues of causation without hearing expert testimony. But  ‘[w]here the complexity of the causation issue is beyond common experience, expert testimony is required to establish causation.’ ” (Webster v. Claremont Yoga (2018) 26 Cal.App.5th 284, 290 [236 Cal.Rptr.3d 802], internal citation omitted.)

“The Supreme Court … set forth explicit guidelines for plaintiffs attempting to allege injury resulting from exposure to toxic materials: A plaintiff must ‘allege that he was exposed to each of the toxic materials claimed to have caused a specific illness’; ‘identify each product that allegedly caused the injury’; allege ‘the toxins entered his body’ ‘as a result of the exposure’; allege that ‘he suffers from a specific illness, and that each toxin that entered his body was a substantial factor in bringing about, prolonging, or aggravating that illness’; and, finally, allege that ‘each toxin he absorbed was manufactured or supplied by a named defendant.’ ” (Jones v. ConocoPhillips Co. (2011) 198 Cal.App.4th 1187, 1194 [130 Cal.Rptr.3d 571], quoting Bockrath, supra, 21 Cal.4th at p. 80, footnote omitted.)

“[M]ultiple sufficient causes exist not only when there are two causes each of which is sufficient to cause the harm, but also when there are more than two causes, partial combinations of which are sufficient to cause the harm. As such, the trial court did not err in refusing to instruct the jury with the but-for test.” (Majorsupra, 14 Cal.App.5th at p. 1200.)

Secondary Sources

6 Witkin, Summary of California Law (11th ed. 2017) Torts, §§ 1334–1341
California Tort Guide (Cont.Ed.Bar 3d ed.) §§ 1.13–1.15
1 Levy et al., California Torts, Ch. 2, Causation, § 2.02 (Matthew Bender)
4 California Trial Guide, Unit 90, Closing Argument, § 90.89 (Matthew Bender)
California Products Liability Actions, Ch. 2, Liability for Defective Products, § 2.22, Ch. 7, Proof, § 7.06 (Matthew Bender)
33 California Forms of Pleading and Practice, Ch. 380, Negligence, § 380.71 (Matthew Bender)
16 California Points and Authorities, Ch. 165, Negligence, §§ 165.260–165.263 (Matthew Bender)