Circuit Judge, dissenting.
The district court instructed the jury that it must find in Peabody’s favor if Peabody had proven that it would have terminated Mayall regardless of his age, even if Mayall had also established that age was a “determining factor” in Peabody’s decision.1 This *575was a recipe for confusion. See Hicks v. Brown Group, Inc., 902 F.2d 630, 665 (8th Cir.1990), vacated and remanded on other grounds, 499 U.S. 914, 111 S.Ct. 1299, 113 L.Ed.2d 234 (1991). As our precedents make clear, finding that age was a “determining factor” is equivalent to finding that the plaintiff would not have been terminated “but for” his age. See, e.g., Holzman v. Jaymar-Ruby, Inc., 916 F.2d 1298, 1304 (7th Cir.1990); Oxman v. WLS-TV, 846 F.2d 448, 452 (7th Cir.1988); La Montague v. American Convenience Prod., Inc., 750 F.2d 1405, 1409 (7th Cir.1984); Golomb v. Prudential Ins. Co. of Am., 688 F.2d 547, 551-52 (7th Cir.1982).2 Thus, if a jury accepts the plaintiffs contention that age was a “determining factor” in his discharge, it has necessarily rejected the employer’s contention that it would have terminated the plaintiff regardless of his age; both cannot simultaneously be true.
The district court itself seemed to acknowledge the inherent contradiction, explaining:
You cannot have both of these situations existing in the same case. If he was discharged, if we assume for the sake of discussion that the discharge was made and that his age was a determining factor in the discharge, then it would be an impossibility for the affirmative defense to be proven, so that it’s got to be one or the other, and if he proves that the age was a determining factor, then that’s the end of the case.
Tr. at 246-47. The court nonetheless declined to rephrase the instruction, because “[ujnfortunately as I read these cases, the courts, including the Seventh Circuit have used this language and have said this. I don’t think I can take it on myself to fly in the face of that.” Id. at 247.
In fact, we have never suggested that if age was a “determining” factor in the discharge decision, an employer might still prevail with proof that the plaintiff would have been terminated regardless of his age; that would be inconsistent with the “but for” connotation we have attributed to “determining.” We have stated, as the majority points out (Op. at 573-74), that “once the plaintiff in a civil rights case has shown that a forbidden purpose was a substantial factor in the decision to fire him, the burden shifts to the employer to persuade the court that the plaintiff would have been fired anyway, even if that purpose had not existed.” Visser v. Packer Eng’g Assocs., Inc., 924 F.2d 655, 658 (7th Cir.1991) (en banc) (emphasis added) (citing Price Waterhouse v. Hopkins, 490 U.S. 228, 109 S.Ct. 1775, 104 L.Ed.2d 268 (1989)). But we did not use the word “substantial” in Visser as a casual substitute for “determining.” Proof that age was a “substantial” or “motivating” factor in the discharge decision does not answer the question of whether the plaintiff would have been terminated “but for” his age; within the burden-shifting framework of Price Waterhouse and Visser, that is a separate question altogether.
I am sympathetic to the plight of a district judge called upon to fashion a coherent set of jury instructions that accurately reflects the complex legal principles governing age discrimination claims. See Visser, 924 F.2d at 661 (Flaum, J., dissenting). But I cannot agree with the majority that the district court’s instruction in this case “correctly informed the jury of the applicable law.” Op. at 574. The notion that age can be a “deter*576mining” factor yet not the “but for” cause of the plaintiffs discharge defies both precedent and logic, and yet that is the premise of the district court’s instruction. Nothing in the remainder of the instructions resolved this conundrum. Because the jury was therefore deprived of a proper framework for evaluating the evidence, reversal is mandatory.3
I also disagree that the defendant’s closing remarks were not prejudicial to Mayall. Op. at 573. Peabody’s counsel argued:
[Tjhere are various instructions the court will give you. We obviously have them, I have had them. You will take these with you, so first of all I think I can read them correctly. If I don’t, read them to yourself. You can read and understand them as well as I can. It is unlawful for an employer to terminate an employee who is 40 years or older because of his age. Tell me who did you hear about in this case under 40 that received any different treatment from Mr. Mayall? Nobody. Now if that’s the law, then we have to discriminate against him and treat him differently than people under f0.
Tr. at 275-76 (emphasis supplied). This plainly misstates the law, for the ADEA does not require proof that the defendant treated employees under the age of 40 more favorably than it did the plaintiff. La Montague, 750 F.2d at 1411 n. 4. The majority suggests that Peabody’s counsel was merely arguing, as an evidentiary matter, that younger employees (even those under 40) were not necessarily treated more favorably than Mayall. Op. at 573. But the context of the remark belies that explanation. Peabody’s counsel first recited the standard jury instruction advising that “[i]t is unlawful for an employee to discriminate against an employee who is 40 years of age or older because of his age,” and then explained to the jury that in order for Peabody to be held liable under that rule, “we have to ... treat him differently than people under 40.” Id. (emphasis supplied). Mayall’s counsel promptly objected to this argument (Tr. at 276) and rightly so, but the district court overruled the objection. When Peabody’s counsel made essentially the same argument twice more (Tr. at 277-78, 285), the jury may well have been left with the mistaken impression that Peabody must prevail unless Mayall had proven that he was treated less favorably than employees under the age of 40.
The usual admonition to the jury that it follow the law set forth in the instructions was of no help to Mayall. Nothing in the jury instructions corrected the misimpression conveyed by Peabody’s counsel; indeed, it is *577completely plausible to think that a jury reading (or listening to) the quoted instruction would conclude that counsel’s interpretation was natural and correct. This erroneous view of the law was necessarily prejudicial to Mayall, whose case focused on the company’s decision to retain Lueking, an employee who was thirteen years younger than Mayall but nonetheless over the age of 40. At the same time, I cannot say that the evidence favored Peabody to such an extent that the error was harmless. See Op. at 573. Although the evidence was sufficient to support a verdict in Peabody’s favor, the case certainly was not lopsided. Whether Peabody truly eliminated Mayall’s position and whether age played any role in the decision to discharge Mayall while retaining a younger employee are questions that turn on the credibility of the witnesses, as is so often true in discrimination cases. See La Montague, Inc., 750 F.2d at 1410. Consequently, the repeated and uncorrected misstatement of the law by Peabody’s counsel, coupled with the hopelessly confusing jury instruction, compels a new trial.
I therefore respectfully dissent.
. That is the import of the burden of proof instruction, which advised the jury that "[i]f ... you find from your consideration of all the evidence that any of the propositions the plaintiff is required to prove has not been proved, or that defendant’s affirmative defense has been proved then your verdict should be for the defendant.” *575Tr. at 242 (emphasis supplied). The use of the disjunctive “or” suggests that the jury was required to find for the defendant if the affirmative defense had been proven, even if the plaintiff had also established each of the propositions he was obligated to prove. The same instruction explained that it was Mayall's burden to prove, inter alia, "that [his] age was a determining factor in the defendant's decision to discharge him” and Peabody’s burden to prove "that plaintiff’s employment would have been terminated regardless of his age.” Id. at 241. Reading the instruction as a whole, the jury was thus advised to find for Peabody if Mayall had failed to prove that age was a determining factor or (regardless of whether Mayall had carried this burden) if Peabody had proven that it would have terminated Mayall despite his age.
. Thus, in Golomb, we approved the following jury instruction:
The term "determining factor” means that but for defendant's motive to discriminate against him because of age, plaintiff would not have been demoted.
688 F.2d at 552 n. 2. The record makes clear that the parties and the district court understood the term in exactly the same way here. See Tr. at 216, 217, 219, 237, 248.
. The majority has addressed Mayall's objection to the jury instruction as if it were solely an argument that the instruction imposed an unwarranted burden of proof on him. See Op. at 573-74. Although Mayall does make an argument to this effect (Mayall Br. at 20-22), his first and principal objection is that the instruction was confusing to the extent it suggested that age might not be the "but for" cause of his discharge even if it were a "determining factor” (id. at 17-20). I find this argument compelling for the reasons I have stated, but the majority has overlooked it. As for Mayall's objection to the burden of proof imposed on him by the instruction, I would simply make two brief observations. First, to the extent that the instruction suggested that age must be something more than a "determining factor” in Mayall’s discharge in order for him to prevail, it did impose a burden on Mayall that is inconsistent with precedent, for we have never required that age be anything more than a "determining factor” in order for an ADEA plaintiff to prevail. See, e.g., Golomb, 688 F.2d at 550, 551-52. Second, where more than one reason motivated the plaintiff's discharge, under Price Waterhouse, a plaintiff need only show that age was a “substantial” factor; once he has done so, the burden of persuasion shifts entirely to the employer, who must show that the plaintiff would have been terminated even if age had not been considered. Price Waterhouse, 490 U.S. at 244-45, 258, 109 S.Ct. at 1787-88, 1794 (plurality op.), and 261-79, 109 S.Ct. at 1796-1805 (O'Connor, J. concurring in the judgment); Visser, 924 F.2d at 658. Thus, it is not correct, as the majority seems to suggest, that the plaintiff always retains the obligation to rebut the employer’s affirmative defense. (Op. at 574.) See Berlett v. Cargill, Inc., 780 F.Supp. 560, 562 (N.D.Ill.1991); see also Ostrowski v. Atlantic Mut. Ins. Cos., 968 F.2d 171, 184-186 (2d Cir.1992).
Finally, I agree that the district court normally is not obliged to define "determining factor” for the jury as we suggested in Golomb, 688 F.2d at 552 n. 2. See Op. at 574 & n. 5. I would point out, however, that it is precisely because we would expect the jury to otherwise give the term its ordinary meaning that the instruction at issue here is confusing. "Determining” means "but for.” See Random House Dictionary of the English Language (Unabridged) 542 (2d ed. 1987).