concurring and dissenting:
I am in agreement with the majority opinion, except as to Part IV E, affirming the exclusion of evidence on nonusage of the seat belt.
The judgment of the district court on the products liability claim will be vacated and the matter remanded for a new trial in a manner consistent with this opinion.
*769The defendant was prepared to present expert testimony that the decedent would not have been killed had he been wearing the seat belt in the truck. The trial judge ruled that this evidence should not be submitted to the jury. Thus, the fact finder was denied the opportunity .to consider whether the alleged defect in the truck caused the death or whether it would have brought about some lesser physical harm had the decedent fastened the belt which was readily available.
The decedent’s failure to use the belt did not in any way bring about the collision with the tree. I agree, therefore, that its nonuse did not constitute contributory negligence or assumption of the risk and therefore should not affect the determination of liability. However, the testimony, if accepted by the jury, would be relevant to the amount of damages recoverable. I believe it is erroneous to exclude this evidence.
As the majority opinion indicates, there is a split among the courts on this question-one might say as wide as the continent itself. New York allows the diminution of damages defense, Spier v. Barker, 35 N.Y.2d 444, 363 N.Y.S.2d 916, 323 N.E.2d 164 (1974), and California does not, Horn v. Genera] Motors Corp., 17 Cal.3d 359, 131 Cal.Rptr. 78, 551 P.2d 398 (1976). Scholarly commentary is also divided.1
Mitigation and apportionment of damages are different concepts than contributory or comparative negligence. Contributory negligence frees the defendant from liability and all responsibility for damages. Comparative negligence appraises the factors which caused the impact, collision or similar event and uses the relative degree of fault to reduce the damages. Mitigation or apportionment of damages and avoidable consequences, on the other hand, are directed toward activity (or nonaction) having a direct bearing on the extent of injury but not on the conduct causing the litigated event.
In McCown v. International Harvester Co., 463 Pa. 13, 342 A.2d 381 (1975), the Pennsylvania Supreme Court held that the plaintiff’s careless driving could not be used as a contributory negligence defense to defendant’s liability for manufacturing a dangerously defective truck, nor could it be used to reduce damages. Since the plaintiff’s actions were connected with the happening of the collision, they were relevant only on the matter of responsibility for the accident — not the damages sustained.2 The case, therefore, is not inconsistent with a damage diminution approach.
The monetary result reached by apportioning damages may be the same as in application of comparative negligence but the factors leading there must be distinguished. By way of illustration, it may be helpful to examine the results which could occur in a routine intersection accident case in a state which applies comparative negligence and also apportionment of damages. A jury might well determine that driver A was ten percent at fault for failing to observe driver B going past a stop sign, and also that if driver A had been wearing a seat belt, his damages would have been *770twenty percent less than those actually sustained. Both factors would then be applied to reduce the amount recoverable. Because the same result can be reached under comparative negligence without concern over whether the plaintiff’s conduct goes to liability or damages, there is a tendency to blur the line between them.
The concepts of liability and damages are distinct and must be kept so. There has been no suggestion that Pennsylvania law does not apply the same law of damages in § 402A cases as in negligence actions. Logically, there is just as much responsibility on an injured person to seek medical assistance for a broken leg resulting from a collision caused by a § 402A dangerously defective automobile as one inflicted by a negligently driven car. Apportionment as well as mitigation of damages should be equally applicable. The thrust of § 402A is directed toward establishing liability. It does not purport to change the traditional law of damages which is to be applied once liability has been determined. In my view, whether apportionment of damages is to be applied does not turn on how liability was determined. The rule should apply in strict liability as well as negligence cases.
Restatement (Second) of Torts § 433 provides for apportionment of damages when plaintiff’s conduct was a factor in the harm3 and comment f explains that the doctrine of avoidable consequences is an application of the rule. Because avoidable consequences applies to actions taken after the impact, it has been said to be inapplicable to the seat belt defense. That distinction has not always been observed, however,4 and should not be controlling in this case. Simply because the correct pigeonhole for the legal theory is not immediately apparent does not mean that critical evidence should be disregarded. Its relevance is apparent. The test should be not when the challenged activity or nonactivity took place; rather, the focus should be whether it played a part in producing the event or was totally unrelated to that event and affected only the injury. The inquiry should not be chronological, but causal.
Horn v. General Motors Corp., supra, is not persuasive because it does not distinguish activity related to liability and that going only to damages. The opinion simply equates diminution of damages and contributory negligence without recognition of the differences between them. Spier v. Barker, supra, on the other hand, analyzes the matter at some length and adopts the chronological and causal approach. See the analysis of Spier in 3 Hofstra L.Rev. 883 (1975).5
The underlying theory of strict liability is to make it easier to shift the loss caused by a defective product to the manufacturer *771and, of course, ultimately to his customers. But there is questionable justification in saddling customers with price increases caused by the failure of a plaintiff to minimize damages with the use of proven and practical safety devices.
The seat belt is a protective device which is required by federal regulations to be installed on manufacture of every automobile. Impressive statistical studies show that belts do reduce the severity of injuries 6 and for some years there has been an extensive advertising campaign urging their use. Penalizing nonuse to the extent it enhanced injury would be an added incentive to take advantage of this proven safety feature. To deny a jury the right to consider evidence of this nature is contrary to the national policy requiring installation of seat belts and encouraging their use. The arguments of those who doubt the value of seat belts should be presented to the jury and not used to exclude the evidence initially-
In Huddel v. Levin, 537 F.2d 726 (3d Cir. 1976), we were required to predict how the New Jersey Supreme Court would react to a novel question of liability for enhancement of damages in tort actions. In general, New Jersey law on strict liability is not significantly different from that of Pennsylvania, at least insofar as the issues pertinent to this case are concerned, and hence the rationale of that case is helpful here. In Huddel, the defendant driver negligently drove his automobile into the rear of decedent’s car causing decedent to be thrown against a defective headrest. We held that the manufacturer of the headrest was liable only to the extent that that device enhanced the injuries received in the original impact. We distinguished between the circumstance where the actions of tortfeasors combine contemporaneously to produce a single impact and the situation where injuries were caused by a defective accessory within the car after the original impact had occurred. That same reasoning applies here. The nonuse of the seat belt was a factor which had no causal relationship to the impact but only to the injuries received thereafter.
I am not persuaded by the objection that acceptance of seat belt testimony by a jury will require speculation on the proper amount of damages. It is naive indeed to say that the law does not permit juries to speculate on damages when daily they are asked to determine the value of future pain and suffering. There are few things more uncertain in this world than the length of a particular person’s life, yet juries regularly determine damages in death cases. Indeed, in this very case that problem was submitted to the jury. Damage apportionment in a seat belt case would not be more conjectural.
The jury should have been permitted to consider the evidence of seat belts as bearing on mitigation of damages. I would place the burden on the defendant to prove the elements of mitigation but would not bar the jury from considering this valuable evidence.
. Although the literature is somewhat extensive, the following listing is representative, though not complete: Kircher, The Seat Belt Defense — State of the Law, 53 Marq.L.Rev. 172 (1970); Kleist, The Seat Belt Defense — An Exercise in Sophistry, 18 Hastings L.J. 613 (1966); Snyder, The Seat Belt as a Cause of Injury, 53 Marq.L.Rev. 211 (1970); Note, A Basic Analysis of the Seat Belt Defense, 34 Alb.L.Rev. 593 (1970); Note, Legislative Enactment of the Seat Belt Defense, 58 Iowa L.Rev. 730 (1973); Note, Seat Belts and Contributory Negligence, 12' S.D.L.Rev. 130 (1967); Note, The Seat Belt Defense — The Sophist’s Escape, 41 Temp.L.Q. 126 (1967); and Comment, The Seat Belt Defense — A Valid Instrument of Public Policy, 44 Tenn.L.Rev. 119 (1977). 3 Hofstra L.Rev. 883 (1975) (concerning Spier v. Barker, supra).
. Whether the philosophy which justifies removal of contributory negligence as a defense to a 402A action should also bar reduction of damages under a comparative negligence statute is an issue which is hotly controverted. See V.E. Schwartz, Comparative Negligence § 4.6 at 97-98 (1974). Often the dispute arises because of failure to distinguish between liability and damages. As the majority observes, since the Pennsylvania comparative negligence statute was not in effect at the time the accident in this case occurred, we do not reach that question.
. Restatement (Second) of Torts § 433A states that “[djamages for harm are to be apportioned among two or more causes where (a) there are distinct harms . . . In addition, § 465, comment c states:
“Such apportionment may also be made where the antecedent negligence of the plaintiff is found not to contribute in any way to the original accident or injury, but to be a substantial contributing factor in increasing the harm which ensues.”
See also W. Prosser, Law of Torts § 65 at 424 (4th ed. 1971).
. See 3 Hofstra L.Rev. 883, 893 (1975).
. Many state courts have considered the “seat belt defense” and their determinations have been inconsistent. Compare, e. g., Mount v. McClellan, 91 Ill.App.2d 1, 234 N.E.2d 329 (1968) (seat belt evidence admissible on issue of damages where there is a causal relationship between injuries sustained and failure to use seat belts, but not admissible for determining liability), and Bentzler v. Braun, 34 Wis.2d 362, 149 N.W.2d 626, 639-40 (1967) (evidence of nonusage admissible since common law duty of ordinary care requires seat belt usage), and Sams v. Sams, 247 S.C. 467, 148 S.E.2d 154 (1966) (granting plaintiffs motion to strike seat belt defense held erroneous), with Fischer v. Moore, 183 Colo. 392, 517 P.2d 458 (1973) (en banc) (adoption of seat belt defense rejected as being a matter for the legislature), and King Son Wong v. Carnation Co., 509 S.W.2d 385 (Tex.Civ.App.1974) (seat belt evidence rejected on ground that mitigation of damages has no application to a plaintiff’s conduct which antedated defendant’s negligence), and Lipscomb v. Diamiani, 226 A.2d 914 (Del. Super. 1967) (seat belt defense rejected as being a proper matter for the legislature). See also Derheim v. N. Fiorito Co., 80 Wash.2d 161, 492 P.2d 1030, 1034 n.2 (1972) (en banc); Symposium: The Seat Belt Defense in Practice, 53 Marq.L.Rev. 172-225, apps. A & B at 226-28 (1970).
. See e.g., Comment, The Seat Belt Defense — A Valid Instrument of Public Policy, 44 Tenn.L. Rev. 119, 120-21 (1977).