dissenting:
The majority reverses the judgment of the court of appeals, concluding that the defendant, Gordon, was entitled to an instruction on comparative negligence despite the lack of any evidence introduced at trial supporting this theory. Because I believe that every jury verdict must be grounded in fact, not legal argument, I respectfully dissent.
A party is entitled to a jury instruction only when the instruction is supported by the evidence and is consistent with existing law. Converse v. Zinke, 635 P.2d 882, 888-89 (Colo.1981); Morgan v. Board of Water Works, 837 P.2d 300, 304 (Colo.App.1992). It is error for the trial court to instruct upon a theory or issue of fact not presented by or responsive to the evidence. Houser v. Eckhardt, 168 Colo. 226, 230-31, 450 P.2d 664, 667 (1969); McCaffrey v. Mitchell, 98 Colo. 467, 472, 56 P.2d 926, 928 (1936).
In the case before us, the two parties submitted evidence on mutually exclusive theories of the case. Both claimed that the other party’s negligence was completely responsible for the collision. Gordon presented evidence that he was at a full stop when Benson backed into him, and Benson presented evidence that she was at a full stop when Gordon rear-ended her. No evidence was offered, by cross examination or otherwise, that both parties could have been partially at fault.1
The theory of comparative negligence is applicable only when the evidence would substantiate a finding that both parties are partially at fault. Powell v. City of Ouray, 32 Colo.App. 44, 49, 507 P.2d 1101, 1105 (1973). In the circumstances presented by the present ease, comparative negligence analysis would have required that both cars were moving at the time of the collision. Neither party presented evidence which would support that finding. Hence, the only way a jury could have found comparative negligence would have been to disbelieve both sides of the case, and arrive at a new set of facts showing that both vehicles were moving at the time.
Inferences may be drawn only from facts in evidence; they may not be based on mere speculation, guess, or conjecture as to what might have actually happened. Tyrrell v. Dobbs Inv. Co., 337 F.2d 761, 765 (10th Cir. 1964); In re People in Interest of R.D.S., 183 Colo. 89, 95, 514 P.2d 772, 775 (1973). In Dilts v. Baker, 162 Colo. 568, 427 P.2d 882 (1967), the evidence showed that at least three vehicles had passed through an intersection when the front vehicle stopped for an unknown reason. The middle pickup truck stopped and the tank truck behind it then collided into its rear end. The passenger in the pickup truck sued the driver of the tank truck for injuries. The pickup truck sustained unexplained damage to the front bumper and fender. The plaintiff claimed the damage occurred when the pickup truck tipped forward upon impact. The defendant claimed that the damage could support an argument that the pickup truck collided with the front vehicle and the driver of the truck was thus contributorily negligent. We held that the trial court incorrectly allowed the issue of contributory negligence to go before the jury because the defendant presented no evidence to support that theory. Id. at 571-72, 427 P.2d at 884-85. Where the evidence raises only the possibility of the occurrence of an event and there is no real evidentiary *783foundation for determining that such an event occurred, such a possibility alone is insufficient to constitute a disputed issue. Id. at 571, 427 P.2d at 884. “We cannot affirm a judgment based upon mere possibilities as the law deals only in probability and reasonably established fact.” Id. at 572, 427 P.2d at 884 (citing Widefield Homes, Inc. v. Griego, 160 Colo. 225, 228, 416 P.2d 365, 367 (1966)).
Additionally, in the case before us, the trial judge’s decision to deny an instruction on comparative negligence was based on her determination that there was no evidence upon which a jury could find anything other than an “all or nothing situation” wherein one party was entirely at fault. The trial judge reasoned that a comparative negligence finding would permit the jury to “do anything it wanted.” Hence, the trial judge evaluated the evidence and found no support for the giving of the tendered instruction. The trial court is uniquely situated to evaluate evidence, and decisions of the trial court are accordingly afforded deference by this court. If there is any evidence to support a tendered instruction, the trial judge is to give it. On the other hand, if there is no such evidence, the giving of the instruction would be error. Houser, 168 Colo, at 230-31, 450 P.2d at 667.
In the present case, the lack of any evidence presented to the jury showing that both cars might have been moving when the collision occurred precludes the jury from making a factual inference to the contrary. To allow a comparative negligence instruction is to invite the jury to disbelieve the evidence presented by both sides and instead devise their own version of the facts. Here, the jurors were invited to disbelieve all of each witness’s testimony, leaving no foundation upon which to lay an appropriate verdict.
Jurors are triers, not architects, of fact. The majority decision today uncouples the jury from the facts presented at trial and permits free navigation. Because I -believe that such a step, however small, abridges both the role of the trial judge and that of the jury, I dissent from the majority holding that the trial court erred in refusing to allow Gordon an instruction on comparative negligence.
I am authorized to say that Justice MULLARKEY joins in this dissent.. During cross examination of defense witnesses, an issue was raised as to whether the defendant’s vehicle had stopped in front of the stop sign or behind it. Gordon claims that the jury could have found that he negligently stopped his vehicle in front of the stop sign and that Benson negligently backed her vehicle into his. However, no witness testified that this was what occurred, and furthermore, no guidance was presented to the jury regarding the correct location for stopping at a stop sign.