*643OPINION ANNOUNCING THE JUDGMENT OF THE COURT
ZAPPALA, Justice.This appeal arises out of injuries George Waddle1 sustained as a result of being struck by the vehicle driven by the Appellant, Leslie Nelkin.2 The record facts indicate that on June 8, 1979, Waddle was struck by a vehicle operated by the Appellant while in the course of her employment. Waddle testified that around noon on the day of the occurrence, he made a service repair call for one of his trucks on Wabash Avenue in the West End section of the City of Pittsburgh. He also indicated that he drove a green pickup truck, which was free from any dents or damages, to the service call and that after the occurrence there were two dents behind the driver’s door. As to the occurrence itself, Waddle had no recollection. In addition, Waddle offered the testimony of Leroy Macklin as to what transpired prior to the incident. He testified that Waddle’s pickup truck and his disabled vehicle were parked partially on the curb, one in front of the other, such that the rear of the pickup truck was facing the front end of the disabled tractor trailer. Macklin testified that after Waddle completed his repairs, he observed Waddle walk around the front end of his pickup truck, close the front hood, and proceed toward the driver’s side of his vehicle. Although Macklin did not actually observe the impact, he did hear a thud and observed Waddle flying through the air.
The Appellant testified that she was en route from New York City to Pittsburgh at the time of the occurrence. After flying into Greater Pittsburgh International Airport and renting an automobile, she stopped for lunch between the airport and her appointment in downtown Pittsburgh. *644After lunch, she proceeded on Wabash Avenue en route to the city, stopping once to verify that she was traveling in the correct direction. At the time of the incident, she testified that she was operating a white Thunderbird and traveling between 20 to 25 miles per hour. When she first observed Waddle, she testified that she was no more than 20 feet from him and that his pickup truck and tractor trailer were parked side by side. After striking Waddle, her vehicle was stopped approximately in the middle of the roadway. She also testified that she did not recall if there was any green paint on the right front of her white Thunderbird before or after the accident. Finally, she did not recall using her horn prior to striking Waddle.
After consideration, a jury determined that Waddle was 60 percent at fault while Appellant was only 40 percent at fault, and thus judgment was entered in favor of the Appellant in accordance with comparative negligence.3 On appeal, Superior Court vacated the judgment and remanded for a new trial, 337 Pa.Super. 636, 487 A.2d 443. The basis for the reversal was the trial judge’s refusal to give the following jury instruction:
“Where a plaintiff’s mind is blank as to an accident and all its incidents the presumption is that he did all that the law required him to do and was not guilty of negligence.”
We thereafter, granted the Appellants’ petition for allowance of appeal and now affirm.
At the conclusion of the trial, Waddle requested that the jury be instructed that he was entitled to a presumption of due care because he had no recollection of the accident. There appears no evidence disputing that Waddle was suffering from amnesia. The Appellant successfully argued before the trial court that the instruction was unnecessary since there was testimony regarding the circumstances immediately prior to the incident. In addition, both the trial court and the Appellant agreed that if any error occurred such error was harmless since the trial court properly *645instructed the jury as to the Appellants’ burden of proving contributory negligence. The Superior Court disagreed holding that the evidence did not establish contributory negligence as a matter of law, thus requiring the requested point for charge. The Superior Court, however, did not address the harmless error argument.
In Auel v. White, 389 Pa. 208, 132 A.2d 350 (1957), we set forth the controlling law regarding the issue of the presumption of due care.
Where a plaintiff’s mind is a blank as to an accident and all its incidents, the presumption is that he did all that the law required him to do and was not guilty of contributory negligence. The presumption, however, is a rebuttable one and must give way when the facts as established by plaintiff’s evidence shows that he was guilty of contributory negligence. (Citations omitted)
389 Pa. at 214, 132 A.2d at 353. See also, Kmetz v. Lochiatto, 421 Pa. 363, 219 A.2d 588 (1966). Therefore, having conceded that Waddle was suffering from amnesia, the only issue is whether the evidence offered by Waddle rebutted the presumption of due care. Like the Superior Court, our review finds no such evidence.
Unlike the plaintiff in Auel, or Heath v. Klosterman, 343 Pa. 501, 23 A.2d 209 (1941), Waddle did not call Nelkin as a witness to establish the facts of the occurrence. True, Waddle did call Leroy Macklin as his witness, but his testimony only established facts prior to and subsequent to the actual occurrence. Our review of the evidence offered by Waddle supports his position that his evidence did not establish contributory negligence as a matter of law thereby, rebutting the presumption of due care.
In fact, Appellant’s testimony appears suspect at best, with regard to the occurrence. The Appellant testified that at the time she observed Waddle she was traveling between 20 to 25 miles per hour, yet, she was unable to bring her vehicle to a stop prior to striking Waddle when he was 20 feet in front of her. She further testified that she did not blow her horn to alert Waddle of her presence. Finally, she *646testified that she did not remember a dent in either her automobile or the pickup truck, even though she was driving a rented automobile which is always subject to inspection for damages. Thus, it is clear that under all the facts the trial court could not determine as a matter of law that Waddle was contributorily negligent.4 Accordingly, the trial court erred in failing to give the requested jury instruction.
The only issue that remains is whether the trial error was harmless as the Appellants suggest. The Appellants contend that any error was obviated by the trial court’s instruction to the jury that the Appellants had the burden of establishing Waddle’s contributory negligence.
In Watkins v. Prudential Insurance Co., 315 Pa. 497, 173 A. 644 (1934) Justice Maxey examined in great detail the derivation of a “presumption.” His conclusive statement regarding the applicability of a “presumption” to jury deliberations is apropos.
In the deliberations of the jury there are permissible inferences (sometimes miscalled “presumptions”) rooted in general human experience and which have weight when the evidence, respectively, for and against a fact in issue leaves the jury in a “twilight zone” of doubt as to that fact. Such “presumptions may be looked upon as legally recognized phantoms of logic, flitting in the twilight, but disappearing in the sunshine of actual facts”.
315 Pa. at 512 (paraphrasing Mackowik v. Kansas City, St. J. & C.B.R. Co., 196 Mo. 550, 94 S.W. 256, “Presumptions may be looked on as the bats of the law, flitting in the twilight, but disappearing in the sunshine of actual facts.” While it is clear that a presumption itself is not evidence, it does evolve from facts.
In the appeal now before us, the purpose of the presumption is to establish as a matter of law that Waddle acted with due care. It is not evidence that Waddle acted with due care but only a rule of law, absent any evidence to the *647contrary, that Waddle acted reasonably. Auel, supra and Kmetz, supra. Thus, if any evidence has been presented in plaintiff’s case in chief to establish contributory negligence as a matter of law, then the presumption must fail.
Contributory negligence is an affirmative defense which must be proved by the proponent. Instructions which place the burden of proof upon the proponent is not establishing a fact but rather allocating the burden of establishing that fact. In order to evaluate a party’s conduct, the jury must assess the actions of the party to determine whether he acted with due care. Thus, the presumption satisfies this assessment and provides the basis upon which the jury could conclude that a party acted reasonably. If a party has presented sufficient evidence to rebut the presumption, then the other party is left without any inference to establish the reasonableness of his actions. Although it is incumbent upon a defendant to demonstrate that a plaintiff acted without due care, a plaintiff must still establish that a defendant acted unreasonably. This determination requires a comparison of the actions of both parties. The presumption of due care was created to provide a legal conclusion that if a plaintiff could testify as to the events in question he would have substantiated that a defendant acted unreasonably in comparison to his own actions. Thus, it is quite clear that the presumption of due care serves a separate purpose from that of an instruction allocating the burden of proof.
Furthermore, we must distinguish between the use of the presumption of due care for purposes of testing a court’s ruling on a judgment not withstanding the verdict and a new trial alleging an error in jury instructions. See Yandrich v. Radic, 499 Pa. 271, 453 A.2d 304 (1982), Larsen, J. dissenting. We have held in Watkins, supra, that a presumption itself is not evidence and has no probative evidentiary value. Since a presumption is not probative evidence, a verdict entered solely on a presumption cannot stand because that judgment would not be supported by sufficient evidence.
*648Unlike a judgment not withstanding a verdict, a motion for new trial does not test the verdict itself but the legal proceedings resulting in the verdict. The basis of the new trial is not that the judgment is unsupported by sufficient evidence, but that an alleged trial error affected the verdict. Thus, the fact that a presumption cannot itself support a verdict is irrelevant when determining whether a jury should be instructed as to a presumption of law. Cases such as Watkins are not controlling when determining whether the trial court committed error in failing to give a jury instruction on the presumption of due care.
Having determined that an instruction on the burden of proving contributory negligence does not satisfy the failure to instruct as to the presumption of due care, it is clear that the trial judge’s error cannot be characterized as harmless. As Justice Musmanno poignantly stated in Lobalzo v. Varoli, 409 Pa. 15, 21, 185 A.2d 557, 561 (1962):
When an error in a trial is of such consequence that, like a dash of ink in a can of milk, it cannot be strained out, the only remedy, so that justice may not ingest a tainted fare, is a new trial.
Finally, the Appellants’ argue that the adoption of comparative negligence negates the necessity of the presumption of due care instruction. As previously stated a jury instruction on the presumption of due care serves a different purpose from that of a comparative negligence instruction allocating the burden of proof. The change in our law from barring recovery for a plaintiff who acts negligently to evaluating the extent of a plaintiff’s own negligence in determining the substantial factor in causing the injuries does not obviate the concerns of a plaintiff suffering from amnesia. Comparative negligence only altered how an injury is evaluated not how it is established. Therefore, the adoption of comparative negligence has no effect on the use of the presumption of due care.
Accordingly, we affirm the Order of the Superior Court reversing the judgment of the Court of Common Pleas and granting the Appellee a new trial.
*649LARSEN, J., filed a concurring opinion in which PAPADAKOS, J., joined. McDERMOTT, j., filed a concurring opinion. NIX, C.J., filed a dissenting opinion in which FLAHERTY and HUTCHINSON, JJ., joined. FLAHERTY and HUTCHINSON, JJ., filed a dissenting opinion.. The Appellee’s husband, George W. Waddle, apparently did not die as a result of injuries suffered in this accident. He died from unrelated causes after filing his appeal to Superior Court.
. Since the Appellant, Columbia Pictures Industries, Inc., is involved in this lawsuit only as the employer of Nelkin, references to the individual Appellant will only mean Nelkin.
. Act of April 28, 1978, P.L. 202, No. 53 § 10(89), 42 Pa.C.S. § 7102 as amended.
. It is interesting to note that in fact the trial judge correctly refused to direct a verdict of contributory negligence.