¶ 1. Joseph D. Meyer appeals from a judgment of divorce awarding his wife, Julia M. Meyer, $1,700 per month in maintenance payments for eight years. Joseph asserts that the trial court erroneously exercised its discretion by considering Julia and his non-marital relationship when it made its maintenance determination. We agree. Therefore, we reverse and remand with instructions to exclude consideration of Julia and Joseph's premarital relationship from the maintenance decision. Joseph also argues that the trial court cannot, in the alternative, base its award on Julia's claim for unjust enrichment. Because a medical degree is not an asset for purposes of an unjust enrichment claim, we agree.
I. Background
¶ 2. Julia and Joseph met in March of 1985 in Green Bay. At the end of that summer, Joseph began attending college at the University of Wisconsin-Green Bay. He began spending the night at Julia's apartment in Green Bay in February 1986. While Joseph attended school, Julia worked, first as a nurse, and then, beginning in December 1988, as a claims examiner at an insurance company. Joseph worked during the summers while in college, but Julia testified that she paid all of the rent, telephone and utility expenses for her apartment.
¶ 3. In August 1989, Julia and Joseph moved to Milwaukee so that he could attend medical school. In their first year in Milwaukee, they rented an apart*195ment together, but in 1990 they moved into a house. Joseph testified that his mother purchased the house and that he and Julia made monthly payments to his mother out of their joint checking account. In 1992, Joseph and Julia purchased a duplex, and lived in one half while renting out the other half. While Joseph attended medical school, Julia continued to work in the insurance industry. She testified that she also did the majority of the housework and ran all of the household errands. Joseph paid for his college and medical school tuition and books with loans.
¶ 4. Julia and Joseph married in May 1993. Joseph graduated from medical school in 1994. In May of that year, he and Julia moved to La Crosse so that he could begin his residency program. After their first child was born, Julia began working for an insurance company in La Crosse. She also took primary responsibility for caring for their child. Joseph completed his residency in 1997 and began working as an urgent care doctor at a clinic in La Crosse.
¶ 5. In June 1997, Julia filed a petition for divorce. In September 1998, she filed an amended petition for divorce to include a claim for unjust enrichment based on her support of Joseph while he obtained his medical degree. The trial court concluded that if Julia proved the elements of unjust enrichment, it would address Julia's premarital support of Joseph and resolve the unjust enrichment claim within the divorce.
¶ 6. At trial, Julia testified that, before she met Joseph, she intended to go back to school to get a degree in business administration. After she became seriously involved with Joseph, she said her plans changed. She testified that she knew that they could not both go to school full time and that she understood that, based on *196the commitment they made to each other, they would both benefit once he began earning a doctor's .salary. Julia asked the trial court to award her $2,400 per month in maintenance for five years.
¶ 7. At the close of trial, the court granted the judgment of divorce. It did not make a specific ruling on Julia's unjust enrichment claim. The court stated that while
an unjust enrichment claim may be held because I do not believe that a piece of property is necessary ... I do believe that, standing by itself, the contribution of Mrs. Meyer to the education, training, and increased earning capacity of Dr. Meyer is sufficient without the unjust enrichment claim to provide her some compensation under a fairness and equity argument in this case.
¶ 8. The court awarded Julia $1,700 per month in maintenance for a period of eight years. It reasoned that $1,700 per month would allow Julia to support herself and her child, and to go to school. The court explained:
I'm satisfied that $1,700 is a reasonable sum to award for maintenance, taking into consideration all of the factors which this Court must consider, including the contribution which she has provided to his earning capacity.
The length of the support — Dr. Meyer is correct that this is only a four-year marriage for these parties. And under what would normally be looking at this strictly by the numbers type of situation, the child support — or the maintenance would not be for a long period of time.
But these parties, based upon my findings, have cohabited for the major part of 1987, '88, ’89, *197'90, '91, '92, '93, '94, '95 and '96. So that's approximately ten years. Some of that they were married. Some of that they were not. But, in taking into consideration the total consequences of how they came together and the length of period of time they were together and the contribution that she has made to this marriage, the Court is satisfied that a maintenance award in the amount of [$1,700] for a period of eight years is a reasonable award.
Joseph appeals.
II. Analysis
A. Maintenance Award
¶ 9. Joseph contends that the trial court erred by considering Julia and his non-marital relationship in making its maintenance decision. The determination of the amount and duration of maintenance rests within the discretion of the trial court. See Olski v. Olski, 197 Wis. 2d 237, 242 n.2, 540 N.W.2d 412, 414 n.2 (1995). We will not overturn a trial court's maintenance decision unless the court erroneously exercised its discretion by failing to consider relevant factors, basing its award on factual errors, making an error of law, or granting an excessive or inadequate award. See id.
¶ 10. In Watts v. Watts, the supreme court held that Wisconsin's property division statute, § 767.255, Stats., did not extend to unmarried cohabitants. Watts v. Watts, 137 Wis. 2d 506, 517-18, 405 N.W.2d 303, 308 (1987). The court noted that the legislature intended the Family Code to apply, "for the most part, to those couples who have been joined in marriage according to *198law." Id. at 519, 405 N.W.2d at 309. The court concluded:
Furthermore, the Family Code emphasizes marriage. The entire Family Code, of which ch. 767 is an integral part, is governed generally by the provisions of sec. 765.001(2), which states in part that "[i]t is the intent of chs. 765 to 768 to promote the stability and best interests of marriage and the family .... Marriage is the institution that is the foundation of family and of society. Its stability is basic to morality and civilization, and of vital interest to society and the state." (Emphasis supplied.) Section 765.001(3) further states that "[c]hapters 765 to 768 shall be liberally construed to effect the objectives of sub. (2)." The conclusion is almost inescapable from this language in sec. 765.001(2), (3) that the legislature not only intended chs. 765-768 to protect and promote the "family," but also intended "family" to be within the "marriage" context.10
*199¶ 11. Based on Watts, in Greenwald v. Green-wald, we concluded that one spouse's premarital contributions to the other spouse's estate was not relevant to a maintenance claim. Greenwald v. Greenwald, 154 Wis. 2d 767, 790, 454 N.W.2d 34, 42-43 (Ct. App. 1990). In Greenwald, a retired widower hired a housekeeper, who lived with him for ten years while taking care of his home before the two married. Id. at 776-77, 454 N.W.2d at 37. We decided that Watts precluded the trial court from considering the contributions the housekeeper made during the ten-year premarital relationship in its maintenance determination. See id. at 789-90, 454 N.W.2d at 42-43.
¶ 12. In Greenwald, we did not simply affirm a trial court's discretionary determination. We did not say in Greenwald, "The trial court did not erroneously exercise its discretion when it did not consider Josephine's premarital contributions." Instead, we held as a matter of law that a trial court may not consider premarital contributions in its maintenance and property division determinations. We said:
Although Watts did not present a maintenance claim, we are persuaded that Watts also requires us to reject Josephine's claim that her premarital contribution to Darwin's estate is a relevant factor on her maintenance claim. After examining the Family Code's legislative history in Watts, the supreme court concluded that the code did not govern property divisions between unmarried cohabitants. We conclude that this same reasoning applies with equal force to Josephine's maintenance claim.
Id. at 790, 454 N.W.2d at 42-43 (emphasis added). We conclude that the trial court erroneously exercised its *200discretion by considering Julia and Joseph’s pre-mari-tal relationship when it made its maintenance determination, contrary to our holding in Greenwald.
¶ 13. Julia argues that the trial court's reasoning was correct because, under Wolski v. Wolski, 210 Wis. 2d 183, 565 N.W.2d 196 (Ct. App. 1997), if a couple has been together for a long period, it would be unfair not to consider the entire time they were together in making a maintenance award. However, in Wolski, the parties were married for nearly twenty years, got divorced, remarried for another three years, and then divorced again. Id. at 186, 565 N.W.2d at 197. We held that "[w]hen parties have been married to one another more than once, a trial court, in its exercise of discretion, can properly look at the total number of years of the marriage when considering maintenance for one of the parties." Id. at 192, 565 N.W.2d at 199. Wolski applies only to years of marriage. It does not allow a trial court to consider the time a couple cohabits.
B. Unjust Enrichment
¶ 14. The trial court did not base its decision on Julia's unjust enrichment claim. However, the parties have briefed whether the trial court could have done so and we will address the issue.
¶ 15. Joseph argues that the trial court incorrectly concluded that, in the absence of its maintenance decision, it could have based its award on Julia's unjust enrichment claim. In Wisconsin, "unmarried cohabitants may raise claims based upon unjust enrichment following the termination of their relationships where one of the parties attempts to retain an unreasonable amount of the property acquired through the efforts of both." Watts, 137 Wis. 2d at 532-33, 405 N.W.2d at 314. *201The elements of unjust enrichment are: "(1) a benefit conferred on the defendant by the plaintiff, (2) appreciation or knowledge by the defendant of the benefit, and (3) acceptance or retention of the benefit by the defendant under circumstances making it inequitable for the defendant to retain the benefit." Id. at 531, 405 N.W.2d at 313.
¶ 16. We have interpreted the theory of unjust enrichment to require "that the complaining party present proof of specific contributions that directly led to an increase in assets or an accumulation of wealth." Ward v. Jahnke, 220 Wis. 2d 539, 547-48, 583 N.W.2d 656, 660 (Ct. App. 1998). Thus, in a non-marital cohabitation situation, for the complaining party to recover under an unjust enrichment claim, he or she must demonstrate: "(1) an accumulation of assets, (2) acquired through the efforts of the claimant and the other party and (3) retained by the other party in an unreasonable amount." Waage v. Borer, 188 Wis. 2d 324, 329-330, 525 N.W.2d 96, 98 (Ct. App. 1994). Whether the facts of this case satisfy the legal standard for unjust enrichment is a question of law that we review de novo. See id. at 328, 525 N.W.2d at 98.
¶ 17. Joseph asserts that Julia's unjust enrichment claim cannot succeed because she has not shown an accumulation of assets. He points out that Julia's claim is based on her support while he obtained a medical degree. In Dewitt v. Dewitt, we concluded that a trial court could not value a law degree as an asset to be included in a marital estate. DeWitt v. DeWitt, 98 Wis. 2d 44, 53, 296 N.W.2d 761, 765 (Ct. App. 1980). Joseph argues that, similarly, in an unjust enrichment case, an educational degree does not meet the requirement *202of showing an increase in assets or an accumulation of wealth.
¶ 18. Julia argues that DeWitt is inapplicable in this case. She points out that in Lundberg v. Lundberg, 107 Wis. 2d 1, 318 N.W.2d 918 (1982), and Roberto v. Brown, 107 Wis. 2d 17, 318 N.W.2d 358 (1982), the supreme court held "that DeWitt, which involved the [divorce] statutes as they existed prior to the 1977 Divorce Reform Act, was not controlling for cases arising after the Act." Id. at 22, 318 N.W.2d at 360. In Lundberg, the court stated that, in that case, a medical degree was "[i]n a sense ... the most significant asset of the marriage." Lundberg, 107 Wis. 2d at 14, 318 N.W.2d at 924. It concluded that, when one spouse supports the other spouse through school, the first spouse can be compensated through property division and maintenance. See id. at 10, 318 N.W.2d at 922.
¶ 19. We agree with Joseph that a degree is not an asset for purposes of unjust enrichment. Although DeWitt involved the valuation of a degree as an asset within a marital estate, our reasoning in that case also applies in cases of unjust enrichment. In DeWitt, we pointed to the difficulty of placing a value on a degree:
Whether a professional education is and will be of future value to its recipient is a matter resting on factors which are at best difficult to anticipate or measure. A person qualified by education for a given profession may choose not to practice it, may fail at it, or may practice in a specialty, location or manner which generates less than the average income enjoyed by fellow professionals. The potential worth of the education may never be realized for these or many other reasons.
*203DeWitt, 98 Wis. 2d at 58, 296 N.W.2d at 768 (footnote omitted). It would be difficult for the trial court to fairly estimate the value of Joseph's medical degree in order to evaluate Julia's unjust enrichment claim. Although Joseph used his medical degree to obtain work as a doctor at a clinic with a fixed salary, it would be unfair to use that salary as a basis for valuing his degree because there is no guarantee that he will keep that job or its salary.
¶ 20. Our holding in DeWitt is exemplified in this case. The trial court made no determination that Joseph's degree was or was not property. It did not value the degree. Julia's expert witness illustrated our concern in DeWitt. Depending upon the method he used, the expert valued Julia's loss or Joseph's benefit as between $47,543 and $522,861. Though legally trained persons are comfortable with making or approving an award somewhere between these values, most members of the lay public would view such an award as something akin to a lottery.
¶ 21. We do not agree with Julia that Lundberg and Roberto have rendered our conclusion in DeWitt inapplicable in this case. In Lundberg and Roberto, the supreme court concluded that the changes to the divorce statutes brought by the 1977 Divorce Reform Act gave a trial court the flexibility to compensate a spouse who supported the other spouse through school. Lundberg, 107 Wis. 2d at 9-10, 318 N.W.2d at 922. Thus, the court concluded that our holding in DeWitt did not apply to cases arising after the Divorce Reform Act. See Roberto, 107 Wis. 2d at 22, 318 N.W.2d at 360. However, an unjust enrichment claim is an action in "quasi contract." See Watts, 137 Wis. 2d at 530, 405 N.W.2d at 313. It is not an action based on divorce laws. A change in the divorce statutes does not render *204our reasoning in DeWitt inapplicable to a claim based upon unjust enrichment. In Lundberg and Roberto, the supreme court did not address whether an educational degree could be considered an asset. DeWitt remains the only case to address that issue.
¶ 22. Cook v. Cook, 208 Wis. 2d 166, 189 — 90, 560 N.W.2d 246, 256 (1997), holds that the court of appeals lacks subject matter jurisdiction to overrule, modify or withdraw language from one of its published opinions.1 Only the supreme court has the power to overrule or modify DeWitt. Because placing a value on a degree would be as difficult here as it was in DeWitt, we conclude that Julia cannot state a claim for unjust enrichment based on her contributions to Joseph's medical degree.2
¶ 23. The court of appeals is primarily an error correcting court. See State ex rel. Swan v. Elections Board, 133 Wis. 2d 87, 94, 394 N.W.2d 732, 735 (1986). *205We are bound by both the prior decisions of this court, see Cook, 208 Wis. 2d at 190, 560 N.W.2d at 256, and of the supreme court, see State v. Olsen, 99 Wis. 2d 572, 583, 299 N.W.2d 632, 638 (Ct. App. 1980). The supreme court, see Swan, 133 Wis. 2d at 93-94, 394 N.W.2d at 735, and the legislature, see Rice v. City of Oshkosh, 148 Wis. 2d 78, 91, 435 N.W.2d 252, 257 (1989), are the governmental bodies designed and authorized to decide the public policy of the State of Wisconsin. There are few issues as policy laden as the proper place of cohabitants in Wisconsin law. The supreme court recognized the nature of this issue in Watts, 137 Wis. 2d at 517 n.6 and 519 nn. 10 — 11, 405 N.W.2d at 308 n.6 and 309 nn.10-11. Cohabitation, whether government should recognize cohabitants in the same way it recognizes married couples, whether the sexual orientation of cohabitants is relevant in a divorce setting, and whether cohabitants should be permitted to divorce each other are topics debated with fervor in today's society. This court is not the place to decide the public policy regarding these issues. We reject the entreaties of Julia and the dissent to do so.
¶ 24. For the reasons discussed above, we reverse. We remand with directions to exclude the time the parties cohabited from the trial court's maintenance determination, and for further proceedings consistent with this opinion.
By the Court. — Judgment reversed and cause remanded with directions.
When the legislature abolished criminal sanctions for cohabitation in 1983, it nevertheless added a section to the criminal code stating that while the state does not regulate private sexual activity of consenting adults, the state does not condone or encourage sexual conduct outside the institution of marriage. The legislature adopted the language of sec. 765.001 that "[mjarriage is the foundation of family and society. Its stability is basic to morality and civilization, and of vital interest to society and this state." Sec. 944.01, Stats. 1985-86.
Id. at 518-19, 405 N.W.2d at 308-09. We cannot conclude that, despite this holding in Watts, the Family Code somehow applies to the Meyers' cohabitation period.
Subject matter jurisdiction is the power of a court to hear and decide a particular case or controversy. See P.C. v. C.C., 161 Wis. 2d 277, 297, 468 N.W.2d 190, 198 (1991).
Our conclusion comports with other Wisconsin cases involving claims of unjust enrichment based on personal relationships. In those cases, when the claimant successfully stated a claim for unjust enrichment, it involved quantifiable assets. See Lawlis v. Thompson, 137 Wis. 2d 490, 492—93, 405 N.W.2d 317, 317 (1987) (cash transfers made to the other party); Watts v. Watts, 137 Wis. 2d 506, 514, 405 N.W.2d 303, 307 (1987) (increase in personal and business wealth); Ward v. Jahnke, 220 Wis. 2d 539, 550-51, 583 N.W.2d 656, 661 (Ct. App. 1998) ($11,000 down payment on a house). Cf. Waage v. Borer, 188 Wis. 2d 324, 330-31, 525 N.W.2d 96, 98-99 (Ct. App. 1994) (holding that a claim for unjust enrichment cannot be based on unfulfilled emotional expectations with no proof of accumulated assets).