¶ 96. (dissenting). While I agree with the majority that the circuit court properly excluded the proffered testimony regarding the remotely conceivable complications that could occur if Martindale opted to undergo TMJ surgery, I do not join the majority's conclusion that the circuit court erroneously exercised its discretion by excluding Dr. Ryan's *118proffered testimony and diagram regarding the "mechanism" by which Martindale allegedly was injured. Accordingly, I dissent.
HH
¶97. As the majority explains, the question of whether a witness is qualified under Wis. Stat. § 907.02 (1997-98)1 to provide an expert opinion is a matter left to the sound discretion of the circuit court. Majority op. at ¶¶ 44-45; see also State v. Watson, 227 Wis. 2d 167, 186, 595 N.W.2d 403 (1999). When reviewing a circuit court's decision on a discretionary matter, this court should not examine whether we would have reached the same conclusion as the circuit court. State v. Wollman, 86 Wis. 2d 459, 464, 273 N.W.2d 225 (1979); see also majority op. at ¶ 86. Rather, the appropriate scope of our review is much more limited: "We review a discretionary decision only to determine whether the [circuit] court examined the facts of record, applied a proper legal standard, and, using a rational process, reached a reasonable conclusion. This court will not reverse unless the circuit court's use of discretion is wholly unreasonable." Watson, 227 Wis. 2d at 186 (quotation and citation omitted); see also majority op. at ¶ 28. Indeed, we generally look for reasons to sustain a circuit court's determination on discretionary matters. Schauer v. DeNeveu Homeowners Ass'n, 194 Wis. 2d 62, 71, 533 N.W.2d 470 (1995).
¶ 98. Although the majority in this case professes to adhere to this standard of review, it nonetheless fails to explain on what legal basis the circuit court erred in excluding Dr. Ryan's proffered testimony. Instead, the *119majority simply reexamines the facts in the record and substitutes its own judgment for the sound discretion of the circuit court.
¶ 99. Had the majority reviewed this case in light of the standard of review that it ostensibly applies, it properly would have concluded that the circuit court reasonably exercised its discretion in excluding Dr. Ryan's proffered evidence regarding the possible "mechanism" by which Martindale may have been injured. The circuit court provided two bases for its decision, both of which are legally sound and either of which should have provided grounds for this court to uphold the circuit court's ruling.
A
¶ 100. First, the circuit court ruled that Dr. Ryan's testimony lacked foundation. As this court previously has explained, a judge may insist that an expert opinion be supported by some foundation in the record. Rabota v. Dohner, 45 Wis. 2d 111, 134-35, 172 N.W.2d 409 (1969); see also Wis. Stat. § 904.03 ("Although relevant, evidence may be excluded if its probative value is substantially outweighed by the danger of.. .misleading the jury....").
¶ 101. In the present case, Martindale attempted to introduce: (1) a diagram allegedly depicting how his head and jaw moved during his accident; and (2) Dr. Ryan's testimony explaining the diagram. Although Dr. Ryan stated that he believed that the diagram accurately depicted Martindale's head and jaw movement, his factual foundation for his belief was extremely limited. As he testified:
Well, I do know which kind of automobile [Martin-dale] was in. He was in a Bonneville. And I also *120know that he testified that his — his headrest was too low for his head and that this would depict what could happen in a whiplash injury and I have no other reason to believe that he had an injury to his jaw other than the whiplash injury in this accident. And since I've already testified that I think the accident caused this problem, this is the mechanism of — I believe — causes internal joint derangement.
Thus, in his own words, Dr. Ryan's belief was based on his opinion that the accident caused Martindale's TMJ injury and Martindale's statements regarding his automobile and whiplash injury.
¶ 102. Dr. Ryan's opinion about the cause of Mar-tindale's TMJ injury does not provide an evidentiary basis for his hypothesis regarding how Martindale's head and jaw moved during the accident. To be sure, Dr. Ryan testified without objection that in his opinion, the accident caused Martindale's TMJ. injury. This opinion, however, was not based on Dr. Ryan's firsthand knowledge of the accident or Dr. Ryan's understanding of kinematics, physics, or accident reconstruction. Rather, it was simply a matter of common sense deduction based on the facts available to Dr. Ryan. As his testimony indicates, Dr. Ryan began with the factual premises that Martindale had a TMJ injury and was involved in an accident; he then ruled out possible causes for the injury other than Martindale's accident. Syllogistically, Dr. Ryan's reasoning was as follows:
(1) Martindale had a TMJ injury.
(2) Martindale was in an accident that caused a whiplash injury.
(3) Whiplash injuries are caused by head movement.
*121(4) Head movement can cause TMJ injuries.
(5) Thus, the head movement in the accident could have caused Martindale's TMJ injury.
(6) Dr. Ryan knew of no other possible cause for Martindale's TMJ injury.
(7) Therefore, Dr. Ryan opined that the head movement in the accident caused Martin-dale's TMJ injury.
At best, this reasoning indicates that Dr. Ryan knew that Martindale's head moved in the accident. But none of this reasoning indicates that Dr. Ryan knew how Martindale's head and jaw moved in the accident.
¶ 103. Further, Dr. Ryan's knowledge of Martin-dale's testimony does not support a conclusion that Dr. Ryan knew how Martindale's head and jaw moved in the accident. Martindale testified about the type of car he was driving and the general facts surrounding his whiplash injury, but he did not explain how his head and jaw moved in the accident with enough precision to allow Dr. Ryan to create a diagram and use it to depict the exact head and jaw movements.
¶ 104. Because Dr. Ryan did not provide any other basis for his opinion, the circuit court reasonably concluded that his diagram and testimony allegedly explaining the exact nature of Martindale's head and jaw movements lacked foundation. Accordingly, the circuit court did not erroneously exercise its discretion in excluding this proffered evidence.
B
¶ 105. Second, the circuit court ruled that Dr. Ryan's testimony was not given to a reasonable degree of medical probability. Medical opinions must be based on a reasonable degree of probability, not upon mere *122possibility, conjecture, or speculation. Pucci v. Rausch, 51 Wis. 2d 513, 518-1.9, 187 N.W.2d 138 (1971). Although there are "[n]o particular words of art" that a medical expert must employ in relating his or her opinion, Drexler v. All American Life & Cas. Co., 72 Wis. 2d 420, 432, 241 N.W.2d 401 (1976), this court has made it clear that" 'might' or 'could' is not sufficient and does not reach the certitude required." Pucci, 51 Wis. 2d at 519.
¶ 106. In the case at hand, Dr. Ryan expressed his opinion regarding Martindale's head and jaw movements in terms of mere possibility, conjecture, or speculation: "[T]his would depict what could happen in a whiplash injury." (Emphasis added.) Dr. Ryan did not explain whether there are other types of whiplash injuries that involve different head and/or jaw movements, and, if so, whether those types of whiplash injuries can cause TMJ injuries. Nor did he attempt to explain with what frequency the type of movement depicted in his diagram actually causes TMJ injury. Rather, Dr. Ryan merely asserted in uncertain terms that the movements shown in his diagram could have occurred in the accident at issue and, if so, Martindale's TMJ injury could have resulted. This does not reach the required level of certitude necessary to form an admissible opinion.
¶ 107. The majority attempts to make an end-run around this shortcoming by scouring Dr. Ryan's deposition transcript for testimony that did reach the requisite degree of certitude. As a result of its efforts, the majority does manage to find such testimony: twenty-six pages and seventy-five questions earlier in the transcript, Dr. Ryan testified "to a reasonable degree of probability" that in his opinion, Martindale's accident had caused the TMJ injury. See majority op. at
*123¶ 67 (quotation omitted). As explained above, this testimony is not disputed. But as also explained above, it does not follow from this testimony that Dr. Ryan had knowledge about how Martindale's head and jaw allegedly moved during the accident sufficient to warrant introducing Dr. Ryan's "mechanism" diagram and testimony to the jury.
¶ 108. The fact remains that with regard to the testimony and diagram at issue (not another question at another point in Dr. Ryan's testimony), Dr. Ryan failed to testify with the requisite degree of certainty. He provided the opinion at issue only in terms of possibility, conjecture, and speculation — as what could have happened. As such, the circuit court reasonably concluded that Dr. Ryan's diagram and testimony should be excluded. Accordingly, as with the foundation ruling discussed above, the circuit court did not erroneously exercise its discretion.
I — I HH
¶ 109. Seemingly driven by a desired outcome rather than its professed adherence to the appropriate standard of review, the majority ignores the circuit court's reasoning and, instead, engages in legal gymnastics. First, rather than initially finding that the circuit court's ruling was in error, the majority begins its analysis with a harmless error standard. As the majority explains, "[a]fter recognizing Dr. Ryan's credentials, permitting him to testify as an expert, and allowing him to give his opinion as to the cause of Martindale's medical condition, the court denied [Dr. Ryan] the ability to explain the 'mechanism' that prompted him to reach his conclusion." Majority op. at ¶ 46. In light of these facts, the majority suggests that Martindale was prejudiced because the jury never *124received an explanation of how a whiplash injury can relate to a TMJ injury. Id. Thus, the majority suggests that the circuit court ruling affected the substantial rights of Martindale without first finding that the ruling was incorrect.
¶ 110. The majority's analysis is flawed. Not only does the majority's analysis beg the questions of whether Dr. Ryan's "mechanism" diagram and testimony lacked foundation and/or the requisite degree of certainty, but it is based on circular logic. In effect, the majority's logic is that the circuit court's ruling was in error because it was not harmless error (i.e., it affected Martindale's substantial rights). Pursuant to this prejudice-first analysis, even if the majority had concluded that the circuit court ruling was correct and was the only reasonable ruling in this case, so long as the ruling could cause Martindale to be prejudiced, the majority would be compelled to reverse. This is not our law.
¶ 111. There is no doubt that Dr. Ryan was an expert. But an expert qualified to testify on one subject is not necessarily qualified to testify on another — even a closely related — subject. See Lemberger v. Koehring Co., 63 Wis. 2d 210, 217-18, 216 N.W.2d 542 (1974). Simply because the circuit court ruled that Dr. Ryan was qualified to provide an opinion regarding the cause of Martindale's TMJ injury, it does not necessarily follow that the circuit court was in error when it concluded that Dr. Ryan was not qualified to opine about the physical mechanics surrounding Martin-dale's alleged head and jaw movement during the accident. As explained above, based on the facts in the record, the circuit court reasonably excluded this latter proffered evidence. Accord Simpsen v. Madison Gen. Hosp., 48 Wis. 2d 498, 510-11, 180 N.W.2d 586 (1970) *125(affirming the circuit court's decision to allow a doctor to testify about injuries, but not about the possible causes of those injuries).2 Consequently, the circuit court's ruling was not in error and the majority should not have reached the harmless error analysis.3
*126¶ 112. And second, the majority puts an irrational spin on the facts of this case. According to the majority, Dr. Ryan "did not try to describe exactly what happened inside Martindale's car. . . .His testimony and the accompanying exhibit were intended to explain to the jury how Dr. Ryan believed Martindale's [alleged] injuries occurred." Majority op. at ¶ 55.
¶ 113. I cannot discern how the majority harmonizes these "facts." On one hand, the majority suggests that Dr. Ryan did not intend to explain how Martin-dale's head and jaw moved during the accident. On the other hand, it suggests that Dr. Ryan intended to explain how he believed Martindale's injuries occurred — i.e., how Martindale's head and jaw moved during the accident. I fail to understand this reasoning. To explain how Martindale's injury occurred by means of anything more than a generic statement that the accident caused Martindale's injury, Dr. Ryan necessarily would have to explain precisely how Martindale's head and jaw moved during the accident. He is not qualified to do so.
¶ 114. For these reasons, I not only am troubled by the fact that the majority has reversed a reasonable discretionary decision by the circuit court, but I also am troubled that the majority has replaced the circuit *127court's reasonable discretionary decision with specious logic and irreconcilable statements of "fact."
I hH h-H
¶ 115. The majority in this case has overstepped the bounds of the appropriate standard of review. This court does not and cannot conclude that the circuit court's ruling was "wholly unreasonable." See Watson, 227 Wis. 2d at 186 (quotation and citation omitted). Rather, at best, the majority simply concludes that the circuit court could have made another "reasonable"^ — albeit less reasonable — ruling. Thus, in the place of the circuit court's sound discretionary decision, the majority has injected as a matter of law its determination of how, were it the circuit court, it would have decided the question of whether to admit Dr. Ryan's testimony.
¶ 116. I will not join the majority's usurpation of the circuit court's discretionary authority. For this reason, I respectfully dissent.
¶ 117. I am authorized to state that Justice N. PATRICK CROOKS joins this dissent.All subsequent references to the Wisconsin Statutes are to the 1997 — 98 version unless otherwise indicated.
In an attempt to undermine the precedential value of Simpsen v. Madison Gen. Hosp., 48 Wis. 2d 498, 180 N.W.2d 586 (1970), the majority asserts that Simpsen is inapposite to the present case because Simpsen involved a podiatrist while the present case involves an oral surgeon. See majority op. at ¶ 56 n.9. I cannot discern that this negligible factual distinction undermines the precedential value of Simpsen. Simpsen, like the present case, involved a licensed, well-seasoned doctor who had experience in diagnosing and treating the type of injury at issue, who had treated the plaintiff after (and before) she was injured, and who had consulted with another doctor who had treated the plaintiff. Simpsen, 48 Wis. 2d at 509-10. Nevertheless, the circuit court in Simpsen, like the circuit court in the present case, ruled that although the doctor was qualified to testify as an expert regarding some aspects of the plaintiffs injuries, he was not qualified to testify about all aspects of the plaintiffs injuries. Id. at 509. As this court should have done with regard to the circuit court's ruling in the present case, this court affirmed the circuit court's sound discretionary decision in Simpsen. Id. at 511.
As noted above, the mere fact that a witness is qualified to testify as an expert on one issue does not mean that the witness is qualified to testify as an expert on another — even a closely related — issue. Lemberger v. Koehring Co., 63 Wis. 2d 210, 217-18, 216 N.W.2d 542 (1974). The circuit court in the present case, like the circuit court in Simpsen, recognized this rule of law.
As the court of appeals noted, Martindale knew well in advance of the trial that the evidence at issue was not admissible. Martindale v. Ripp, No. 99-0649, unpublished slip op. at ¶ 8 (Wis. Ct. App. Oct. 28, 1999). The circuit court made its ruling on June 8, 1998, approximately three months prior to the Sep*126tember 11,1998, commencement of the trial. With such advance notice that Dr. Ryan's diagram and deposition testimony would be partially excluded, Martindale could have sought to have Dr. Ryan testify at trial in order to bolster his opinion or asked the circuit court to permit another qualified expert to testify. Mar-tindale did not pursue either option. Rather, he chose to try the case without the evidence that he now claims to have needed. In light of these facts and the facts discussed above, I would conclude that it was Martindale's inaction — not the circuit court's ruling — that hurt Martindale's case.