The narrow issue we address on this appeal is the correct standard of proof necessary, in a marriage dissolution action, where a spouse who is at fault attempts to mitigate or excuse that fault, while seeking maintenance, by alleging the mental illness of multiple personality disorder. Believing that the Court of Appeals applied a too limited standard, we reverse.1
*323The parties to this action were married in 1978 and lived together until 1990. The husband worked as an engineer and earned $45,-000 per year. Appellee worked in the home as a homemaker. Until 1988, that is. While a student at Murray State University, she took to herself a lover and engaged in a sustained course of adultery, regularly, telling her husband about it. When the affair ended, appellee “took up” with another man. This dissolution action resulted.
In an effort to erase her admitted fault, appellee introduced medical evidence that she suffered from a condition known as multiple personality disorder (hereinafter MPD). It is a fair inference that both parties’ medical witnesses agree that appellee did suffer from some degree of MPD. Their medical opinion differences will be discussed later. The crux of appellee’s defense to this admitted fault was that the “person” who committed adultery was not the same person who was married to appellant, even though they occupied the same body. This “logic” was termed “psycho-babble” by the dissenting opinion in the Court of Appeals.
The domestic relations commissioner initially found, as a matter of fact, that appellee failed to sustain her burden of proof that she lacked control over her “switching” from one personality to another. Applying standards which required appellee to show by “clear and convincing” evidence that she did not have control of the “switching,” he reduced her request for maintenance of $1,103.23 per month to an amount of $500.00 per month for 48 months.
The trial court affirmed the commissioner, stating:
The Commissioner followed Rutherford v. Rutherford [303 S.C. 424], 401 S.E.2d 177 (S.C.1990). The Court agrees with the commissioner that such rule should be followed as the law in this state except that the standard applied to the “switching” issue is that of a “preponderance of the evidence” and not that of “clear and convincing evidence.”2 Further, the Court agrees with the Commissioner that the petitioner did not show that she lacked the degree of control over her switching into the personality of Andrea that would relieve her from a finding of fault.
The Court of Appeals in a 2-1 decision, its view as follows:
The issue in this case is not whether Toni had a adulterous affair. Admittedly, she did. The issue is not whether she could control either the presence of the personality of “Andrea” or Andrea’s actions once Andrea did appear. Regardless of the amount of “control” Toni had over “switching,” the evidence in this record, particularly that of the expert witnesses, established that a mentally healthy person cannot switch from one personality to another and that Toni, at the time of her affair, was profoundly mentally ill. The issue, as far as maintenance is concerned, is whether Toni’s mental condition excuses her “fault.” Without hesitation we hold it does, (emphasis added.)
In reversing the trial court’s decision and remanding the issue to that court, the Court of Appeals attempted to establish the following “standard” of proof: “a spouse seeking maintenance need only establish a causal link between alleged misconduct and his or her mental condition to overcome any attempt to reduce sums otherwise appropriate.”
In remanding the case, the majority directed the trial court to make an appropriate award without consideration of appellee’s misconduct, and for such duration that is consistent with the treatment for MPD.
It is certainly true that both doctors — that of the appellant and that of the appellee — established the fact that appellee had some degree of MPD. However, the *324evidence of appellant’s doctor clearly shows a disagreement with appellee’s doctor in several key issues. The husband’s physician, contradicted the wife’s physician, and emphasized the following matters: (1) The value of appellee being employed; (2) Her lack of motivation if allowed to be totally dependent on maintenance; (3) The likelihood of her mental condition to deteriorate if she was not required to contribute to her own well-being; (4) Her susceptibility to being “coached” by her doctor; (5) Her definite ability to control her “switching” from one personality to another; (6) Her use of the MPD diagnosis as an excuse for wrongful behavior; and (7) His belief that she was not seriously impaired by her disease.
The impact of the standard adopted by the majority of the Court of Appeals is to adopt no standard. All that is required is to establish a “causal link” between the misconduct and his or her mental condition in order to defend fault. No degree of proof to establish the “causal link” is set forth. No guidance to the fact-finder is given. The door is swung wide open for any type of “mental condition” to negate any kind of fault.
The Court of Appeals — without setting any viable or identifiable standard — and while ignoring the finding of fact by the trial judge that appellant did have some control over the “switching” of personalities (thus clearly indicating that she was not totally or fully controlled by the MPD), declared, as a matter of law that she was mentally ill and that “fact” obviated her admitted fault.
We agree with the trial court that the standard of proof necessary in this case is properly set forth in Rutherford v. Rutherford, 307 S.C. 199, 414 S.E.2d 157 (1992). In that case, the husband brought a divorce action based on the adultery of the wife. As an alternate defense, the wife, at trial, argued that even if she had committed adultery she should not be held responsible due to her suffering from MPD. Analogizing to criminal law, in affirming the standard of proof adopted by the Court of Appeals on rehearing, the South Carolina Court:
A defendant is excused from responsibility for his or her acts only if as a result of his or her mental disease or defect he or she lacks the capacity to distinguish moral or legal right from moral or legal wrong or to recognize the particular act charged as morally or legally wrong ... We are not convinced a lower standard of mental impairment in a divorce action is appropriate ... We also find that the sum degree of mental impairment must he proven to avoid the statutory bar of alimony for an adulterous spouse. Therefore, in order to avoid the husband’s action for divorce on the grounds of adultery and the bar of adultery, the wife hears the burden of proving by the preponderance of the evidence that the time she committed adultery, she was unable to appreciate the wrongfulness of her conduct. Id, 414 S.E.2d at 161. (emphasis added.)
We believe that this standard places a fair burden — i.e., a preponderance of the evidence — upon the spouse at fault, to show the extent to which he or she was mentally ill and that because of the mental illness he or she was not able to appreciate “fault” because of the mental illness.
In the present case, ultimately both the domestic relations commissioner and the trial judge applied this standard. The finding was that the appellant, based on her ability to “switch” personalities, was not under control of the MPD and therefore she was able to appreciate the wrongfulness of her conduct. Under all too familiar legal principles, an appellate court cannot substitute its judgment for that of the fact-finder unless that judgment was clearly erroneous. In this case, the evidence of appellant’s doctor was clearly sufficient to justify the trial court’s finding of fact. This alone justifies reversal of this case.
Moreover, it is the view of a majority of this Court that the “standard” applied by the Court of Appeals was in error, and we believe that the Rutherford standard, as noted, is the correct one.
Under these circumstances, we reverse the decision of the Court of Appeals and reinstate the judgment of the trial court.
LAMBERT, REYNOLDS, SPAIN, and WINTERSHEIMER, JJ., concur. *325STEPHENS, C.J., files a separate concurring opinion. STUMBO, J., would overrule Chapman v. Chapman, Ky., 498 S.W.2d 134 (1973) and concurs with the separate concurring opinion of STEPHENS, C.J. D. SCOTT FURKIN, Special Justice, files a separate dissenting opinion.. As will be seen, we are forced to consider this esoteric area of the law because of the continued viability of the case of Chapman v. Chapman, Ky., 498 S.W.2d 134 (1973), in which this Court’s *323predecessor, by judicial fiat, injected the issue of fault into the law in spite of the legislatively enacted no-fault divorce statute.
The author of the opinion, as will be seen in a separate opinion, believes Chapman to be clearly wrong.
. Although not specifically noted at this point in the trial court’s Order, the commissioner had relied upon the decision of the South Carolina Court of Appeals in its application of the "clear and convincing” standard, but this standard was rejected on rehearing in favor of the “preponderance of the evidence” standard, which Judge Buckingham endorses.