This case presents the following issues for review:
(1) Do the Wisconsin adoption statutes permit a third party to adopt the minor child of the third party's nonmarital partner?
(2) If the Wisconsin adoption statutes prohibit this adoption from taking place, do these statutes violate the constitutional rights of either the minor child or the third party?
On February 17, 1992, Annette G. filed a petition to adopt Angel Lace M., the daughter of Annette's partner, Georgina G. The circuit court for Brown County, the Honorable Richard J. Dietz, denied the petition by order dated April 9,1992. The court of appeals certified the appeal for review by this court. We now affirm the order of the circuit court. We hold that this adoption is not permissible under ch. 48, Stats. We further hold that the relevant provisions of ch. 48 do not violate the constitutional rights of either the minor child or the third party.
Angel was born on March 10,1986. On September 20,1988, Georgina and Terry M. adopted Angel. Georgina and Terry were married at the time of the adoption. They separated in February, 1990, and divorced in June of that same year. Aside from paying court-ordered child support, Terry has played no part in Angel's life since late 1990.
*504In June, 1990, Georgina and Angel began living with Annette. The two women have shared equally in raising Angel since that time. Georgina and Annette symbolically solemnized their commitment to each other by partaking in a marriage-like ceremony in Milwaukee on August 11,1991.1
On February 17, 1992, Annette filed a petition in the Brown county circuit court to adopt Angel. Simultaneously, Georgina filed a petition to terminate Terry's parental rights and a petition for the adoptive placement of Angel with Annette. No party filed a petition to terminate Georgina's parental rights.
Judge Dietz held a hearing on the various petitions on March 25, 1992. At the hearing, Terry signed a statement consenting to the termination of his parental rights and testified that his consent was both voluntary and knowing. The Community Adoption Center filed a report with the court recommending the adoption. In addition, a social worker from the center testified at the hearing that the termination of Terry's parental rights and the adoption of Angel by Annette would be in Angel's best interests.
Based on the testimony and other evidence presented at the hearing, the circuit court determined that the proposed adoption would be in Angel's best interests. However, the court also determined that pursuant to ch. 48, Stats., Annette is not competent to adopt Angel and Angel is not competent to be adopted by Annette. Hence, the court denied each of the petitions by order dated April 9,1992.
*505Annette and Georgina appealed the circuit court's order. The court of appeals certified the appeal for review by this court. We accepted the certification and now affirm the order of the circuit court.2
The petitioners argue that the circuit court should have granted Annette's petition for adoption because the court found that the adoption is in Angel's best interests. See sec. 48.01(2), Stats.3 There is no doubt that a court must find that an adoption is in the best interests of the child before the court may grant the petition for adoption. However, the fact that an adoption — or any other action affecting a child — is in the child's best interests, by itself, does not authorize a court to grant the adoption. This court recognized as much in the context of child custody. In In re Marriage of Groh v. Groh, 110 Wis. 2d 117, 126, 327 N.W.2d 655 (1983), we rejected the argument that a trial court is entitled to impose any conditions on custody as long as the custody order is in the best interests of the child:
If the trial court had the power to make any order it pleased so long as the order could somehow be justified by recitation of the rubric 'in the best *506interests of the children,' the limits the legislature placed on the court's exercise of power in custody matters would be meaningless. Legal custody is subject to the provisions of court orders as sec. 48.02(12), Stats., states. However, it is subject only to orders that the court is empowered to make.
Were we to allow a court to grant an adoption petition any time the adoption is in the best interests of the child, there would be no need for the plethora of adoption statutes other than sec. 48.01(2), Stats. "[A] statute should not be construed so as to render any portion or word surplusage." State v. Ross, 73 Wis. 2d 1, 5, 242 N.W.2d 210 (1976). The petitioners' argument — that a court should grant a petition for adoption as long as it is in the child's best interests — would render several sections of ch. 48 surplusage. Hence, we reject this argument.
"[B]efore a court may make a finding that a second parent adoption is in a child's best interests, it must first determine whether it has the power to grant such an adoption under the existing adoption statutes." Emily C. Patt, Second Parent Adoption: When Crossing the Marital Barrier is in a Child's Best Interests, 3 Berkeley Women's L.J. 96, 111 (1987 — 88) (citing ch. 48, Stats.). "Adoption proceedings, unknown at common law, are of statutory origin and the essential statutory requirements must be substantially met to validate the proceedings." Estate ofTopel, 32 Wis. 2d 223, 229, 145 N.W.2d 162 (1966). Accordingly, before we apply the best interests standard in this case, we must determine whether Annette's proposed adoption of Angel satisfies the statutory requirements for adoption.
*507In Wisconsin, the requirements for adoption are found in ch. 48, Stats. We therefore apply the relevant provisions of ch. 48 to the proposed adoption. The application of a statute to a given set of facts is a question of law. Tahtinen v. MSI Ins. Co., 122 Wis. 2d 158, 166, 361 N.W.2d 673 (1985). Hence, we need not give deference to the decisions of the trial court. Id. Our purpose in interpreting a statute is to give effect to the intent of the legislature, with the plain language of the statute acting as our primary guide. Id.
Section 48.82, Stats.,4 controls who may adopt a minor. A party petitioning to adopt a minor must satisfy two requirements. First, the party must be a resident of Wisconsin. Annette satisfies this first requirement. Second, the party must fit the description from either sec. 48.82(1)(a) or sec. 48.82(1)(&). Annette does not qualify under sec. 48.82(l)(q) because she is not legally "the husband or wife" of Georgina who is the *508"parent of the minor." However, Annette does fit the description in sec. 48.82(1)(&) because she is "[a]n unmarried adult."
For the adoption to be valid, not only must Annette qualify as a party who may adopt Angel, but Angel must also be eligible for adoption. Section 48.81, Stats.,5 controls who may be adopted. A minor must also satisfy two requirements to be eligible for adoption. Angel satisfies the first requirement of the statute because she was present in the state of Wisconsin at the time Annette filed the petition for adoption. See sec. 48.81 (2). It is less clear whether Angel satisfies the second requirement. Pursuant to sec. 48.81 (1), a minor may only be adopted if her "parental rights have been terminated . . .."6 Angel's adoptive father, Terry, has consented to the termination of his parental rights. Georgina's parental rights, on the other hand, remain intact.
The petitioners claim that sec. 48.81(1), Stats., is ambiguous. According to the petitioners, the statute could mean that Angel is eligible for adoption only if *509the rights of both of her parents have been terminated. Or, it could mean that she is eligible for adoption as long as the rights of at least one of her parents have been terminated. The petitioners ask this court to construe the statute liberally to further the best interests of Angel, pursuant to sec. 48.01(2), and accept the second interpretation of the statute.
Under this second interpretation of the statute — that a minor is eligible for adoption as long as the rights of at least one of her parents have been terminated — a minor would be eligible for adoption when the rights of only one of her parents are terminated. The minor would be eligible to be adopted even if the remaining parent is legally fit to raise the child alone and prefers to raise the child alone. Ostensibly, a complete stranger could petition to adopt a minor who is a member of this stable family; and, at least pursuant to sec. 48.81, Stats., the proposed adoption would be permissible. The legislature could not have intended to declare a minor eligible for adoption under those circumstances. This would be an absurd result.7 This court will not construe a statute so as to work absurd or unreasonable results. Estate of Evans, 28 Wis. 2d 97, 101, 135 N.W.2d 832 (1965). Hence, we hold that pursuant to sec. 48.81(1), a minor is not eligible for adoption unless the rights of both of her parents have been terminated.8 Because Georgina's parental rights *510remain intact, Angel is not eligible to be adopted by Annette.
Section 48.92, Stats.,9 also stands in the way of Annette's proposed adoption of Angel. This statute severs the ties between the birth parent10 and the adopted *511minor after a court enters the order of adoption.11 Pursuant to sec. 48.92(2), if the circuit court grants Annette's petition to adopt Angel, "all the rights, duties and other legal consequences of [Georgina's relationship with Angel] shall cease to exist." (Emphasis added.) If the legislature had intended to sanction adoptions by nonmarital partners, it would not have mandated this "cut-off1 of the "rights, duties and other legal consequences" of the birth parents in these adoptions.
The petitioners argue that, despite the use of the word "shall," this "cut-off1 provision is directory, not mandatory, under Wisconsin law.12 " 'Shall' will be construed as directory if necessary to carry out the intent of the legislature." State v. R.R.E., 162 Wis. 2d 698, 707, 470 N.W.2d 283 (1991). This interpretation ignores two basic rules of statutory interpretation. First, "' "shall" is presumed to be mandatory when it appears in a statute.'" State v. Speer, 176 Wis. 2d 1101, 1122, 501 N.W.2d 429 (1993) (quoting American Family Ins. Co. v. Milwaukee, 148 Wis. 2d 280, 285, 435 *512N.W.2d 280 (Ct. App. 1988)). The petitioners' argument does not overcome this presumption. Second, where the legislature specifically enumerates certain exceptions to a statute, this court presumes that the legislature intended to exclude other exceptions based on the rule expressio unius est exclusio alterius. State ex rel. Harris v. Larson, 64 Wis. 2d 521, 527, 219 N.W.2d 335 (1974). ("Under this maxim, if [a] statute specifies one exception to a general rule or assumes to specify the effects of a certain provision, other exceptions or effects are excluded." Black's Law Dictionary 581 (6th ed. 1990)). In this case, the legislature specifically exempted stepparent adoptions by stating that the "cut-off provision applies "unless the birth parent is the spouse of the adoptive parent..See sec. 48.92(2), Stats. This is evidence that the legislature did not intend to exempt other adoptions, including those by nonmarital partners. See Harris, 64 Wis. 2d at 527.
We find more compelling evidence that the "cutoff provision is mandatory when we read the relevent sections of ch. 48, Stats., together. "When multiple statutes are contained in the same chapter and assist in implementing the chapter's goals and policy, the statutes should be read in pari materia13 and harmonized if possible." In Interest of R.W.S., 162 Wis. 2d 862, 871, 471 N.W.2d 16 (1991). (Footnote added.) In this case, reading sec. 48.92 together with secs. 48.81 and 48.82 and harmonizing the three statutes leads to the *513conclusion that the "cut-off' provision of sec. 48.92 is mandatory.
For this court to find that ch. 48, Stats., sanctions the proposed adoption, we must accept the petitioners' interpretation of both secs. 48.81(1) and 48.92(2). The petitioners interpret sec. 48.81(1) as permitting a minor to be adopted as long as the rights of at least one of the minor's parents are terminated. If we accept this interpretation, then a minor who still has one parent could be adopted. Section 48.82(1)(a) clearly allows "[a] husband and wife jointly" to adopt a minor. The petitioners next interpret the "cut-off' provision of sec. 48.92(2) as directory. If we also accept this interpretation, then the above husband and wife could jointly adopt the above minor without severing the ties between the remaining birth parent and the minor. The minor would then have three parents. Subsequently, a court could terminate the rights of one of the three parents and a second husband and wife could jointly adopt the minor, giving the minor four parents. This process could go on ad infinitum. Obviously, the petitioners' interpretations of secs. 48.81(1) and 48.92(2), read in pari materia, could lead to absurd results. This court will not construe a statute so as to work absurd or unreasonable results. Evans, 28 Wis. 2d at 101.
To avoid this absurd result and to harmonize the rules of statutory construction discussed above, we hold that the "cut-off' provision of sec. 48.92(2), Stats., is mandatory. Hence, Georgina would lose the "rights, duties and other legal consequences of' her relationship with Angel if the circuit court granted Annette's petition to adopt Angel. This result would frustrate rather than further the petitioners' intentions. We also *514hold that, pursuant to sec. 48.81(1), Angel is not eligible for adoption. Therefore, we conclude that the proposed adoption does not satisfy the essential requirements of the adoption statutes and is, in fact, prohibited by these statutes.14 The circuit court properly denied the petitions before it despite its finding that the adoption would be in Angel's best interests.
The petitioners next argue that if the relevant provisions of ch. 48, Stats., do not authorize a circuit court to grant this petition for adoption, then these statutory provisions violate the constitutional rights of either *515Angel or Annette or both. The constitutionality of a statute is a question of law which we review de novo. Chappy v. LIRC, 136 Wis. 2d 172, 184, 401 N.W.2d 568 (1987). In reviewing the constitutionality of a statute, "there is a strong presumption that a legislative enactment is constitutional." Id. The party challenging the constitutionality of a statute "must prove beyond a reasonable doubt that the act is unconstitutional." Id. at 185. Furthermore, " 'every presumption must be indulged to sustain the law if at all possible and, wherever doubt exists as to a legislative enactment's constitutionality, it must be resolved in favor of constitutionality.' " Id. (quoting State ex rel. Hammermill Paper Co. v. La Plante, 58 Wis. 2d 32, 46, 205 N.W.2d 784 (1973)).
With this heavy burden in mind, we turn to the petitioners' arguments. The petitioners claim that by prohibiting this adoption, secs. 48.81 and 48.92, Stats., deny Angel her right to due process, guaranteed by the Fourteenth Amendment to the United States Constitution, in two ways. First, the petitioners claim that the statutes deprive Angel of her right to have her best interests be the paramount factor in a court's decision regarding Annette's petition for adoption.
The requirement of due process applies only to deprivations of property or liberty interests. Board of Regents v. Roth, 408 U.S. 564, 569 (1972). The right to have her best interests guide our analysis in this adoption proceeding certainly does not qualify as one of Angel's property interests. In addition, United States Supreme Court jurisprudence makes it clear that this alleged right does not qualify as a liberty interest.
*516An interest will only qualify as a liberty interest if it is both fundamental and traditionally protected by our society. Michael H. v. Gerald D., 491 U.S. 110, 122 (1989) (Scalia, J., plurality). The right to have a child's best interests be the paramount consideration in the adoption proceedings is neither fundamental nor traditionally protected by our society. Adoption itself is not even a fundamental right. Lindley for Lindley v. Sullivan, 889 F.2d 124, 131 (7th Cir. 1989) ("there is no fundamental right to adopt"). It certainly follows that a legislative directive to construe adoption statutes with the child's best interests of paramount consideration is not a fundamental right. Furthermore, because adoption is a relatively recent statutory development, we cannot conclude that adoption has traditionally been protected by our society. Hence, secs. 48.81 and 48.92, Stats., do not deprive Angel of a liberty interest.
In fact, as discussed earlier, the legislature did not intend for this right to attach at all unless the statutory requirements for adoption are satisfied. Because these requirements are not satisfied in this case, Angel never possessed this interest and secs. 48.81 and 48.92, Stats., could not have deprived her of it. We therefore reject this initial attack on the constitutionality of the adoption statutes.
Second, the petitioners argue that by prohibiting this adoption, the relevant statutes deprive Angel of her constitutional right to familial association. Angel's freedom to associate with Annette "receives protection as a fundamental element of personal liberty." See Roberts v. United States Jaycees, 468 U.S. 609, 618 (1984). However, as the petitioners acknowledge, the adoption *517statutes do not prevent Angel from associating with Annette. These statutes merely prevent Annette and Angel from legally formalizing their relationship. This relationship, between a child and her mother's nonmarital partner, is not one that has traditionally received constitutional protection. "The family unit accorded traditional respect in our society, which we have referred to as the 'unitary family,' is typified, of course, by the marital family, but also includes the household of unmarried parents and their children." Michael H., 491 U.S. at 123 n.3. While Angel's relationship with her mother, Georgina, is constitutionally protected because the two form a "unitary family," her relationship with Annette is not. Thus, we reject this second challenge to the constitutionality of Wisconsin's adoption statutes and hold that these statutes do not violate Angel's right to due process.
Amicus curiae, the American Civil Liberties Union of Wisconsin Foundation (ACLU), argues that by prohibiting this adoption, the statutes at issue violate Angel's right to equal protection guaranteed by the Fourteenth Amendment to the United States Constitution. The petitioners join this argument in their reply brief. Both the petitioners and the ACLU claim that the statutory scheme for adoption in Wisconsin sets up two classes of children for the purpose of adoption — children in traditional families and children in nontraditional families. According to this argument, the legislature has chosen to protect the best interests of those children in traditional families while not protecting the best interests of children in nontraditional families.
This argument misinterprets the adoption statutes. The Wisconsin legislature has chosen to *518differentiate between children "whose parental rights have been terminated" and children who still have parents. One exception has been made for children with stepparents. This legislative scheme does not affect a fundamental right and is not based on a suspect classification. Hence, we must declare the statutes constitutional so long as they are rationally related to a legitimate governmental interest. Cleburne v. Cleburne Living Center, 473 U.S. 432, 440 (1985). The Wisconsin adoption statutes are rationally related to the state's interest in protecting the traditional "unitary family." See Michael H., 491 U.S. at 123 n.3. The petitioners and the ACLU have failed to overcome their burden of proving beyond a reasonable doubt that the relevant adoption statutes deprive Angel of her right to equal protection.
Finally, the ACLU claims that by prohibiting this adoption, Wisconsin's legislative adoption scheme violates Annette's right to equal protection by discriminating against her on the basis of her sexual orientation and/or her gender. According to the ACLU, if Annette were involved in a heterosexual relationship or if Annette were a man, she would be able to adopt. Contrary to this claim, Wisconsin's adoption statutes do not discriminate on the basis of sexual orientation or gender. Annette may not adopt Angel because Annette and Georgina are not married. Any legitimate argument the ACLU may have should be directed at Wisconsin's prohibition of same-sex marriages, not the adoption statutes. However, this is not a suit involving marriage and the petitioners have not challenged the state's prohibition of same-sex marriages. The adoption statutes do not violate Annette's right to equal protection. Annette is eligible to adopt a child "whose *519parental rights have been terminated." That is not the case here. In addition, if Annette were married, she would be eligible to adopt the child(ren) of her spouse. Again, that is not the case here. The Wisconsin legislature has enacted a statutory scheme for adoption that balances society's interest in promoting stable, legally recognized families with its interest in promoting the best interests of the children involved. The adoption proposed in this case does not fall within the confines of this constitutionally valid legislative scheme.
We hold that Angel is not eligible for adoption under sec. 48.81(1), Stats., because her parental rights have not been terminated. Furthermore, the proposed adoption is prohibited because sec. 48.92(2) would sever Georgina's ties with Angel. We also hold that the relevant provisions of ch. 48 do not violate the constitutional rights of either Angel or Annette. Therefore, we affirm the circuit court's order that denied the three petitions before the court.
By the Court. — The order of the Brown county circuit court is affirmed.
Wisconsin does not recognize same-sex marriages. See sec. 765.001(2), Stats., Phillips v. Wisconsin Personnel Commission, 167 Wis. 2d 205, 213 n.1, 482 N.W.2d 121 (Ct. App. 1992). Hence, under the laws of Wisconsin, Georgina and Annette are not married. As a result, Annette is not Angel's stepparent.
Though invited by this court, the attorney general declined to participate in this review to defend the order of the circuit court and the constitutionality of the adoption statutes. Therefore, the court appointed the law firm of Foley and Lardner, by Attorney John S. Skilton, to act as respondent-designate and defend those interests.
Section 48.01(2), Stats., provides as follows:
(2) This chapter shall be liberally construed to effect the objectives contained in this section. The best interests of the child shall always be of paramount consideration, but the court shall also consider the interest of the parents or guardian of the child, the interest of the person or persons with whom the child has been placed for adoption and the interests of the public.
Section 48.82, Stats., provides as follows:
48.82 Who may adopt. (1) The following persons are eligible to adopt a minor if they are residents of this state:
(a) A husband and wife jointly, or either the husband or wife if the other spouse is a parent of the minor.
(b) An unmarried adult.
(3) When practicable and if requested by the birth parent, the adoptive parents shall be of the same religious faith as the birth parents of the person to be adopted.
(4) No person may be denied the benefits of this subchapter because of a religious belief in the use of spiritual means through prayer for healing.
(6) Although otherwise qualified, no person shall be denied the benefits of this section because the person is deaf, blind or has other physical handicaps.
(6) No otherwise qualified person may be denied the benefits of this subchapter because of his or her race, color, ancestry or national origin.
Section 48.81, Stats., provides as follows:
48.81 Who may be adopted. Any minor who meets all of the following criteria may be adopted:
(1) Except as provided under s. 48.839 (3) (b) or if an appointment of guardianship has been made under s. 48.831, a minor whose parental rights have been terminated under subch. VIII or in another state or a foreign jurisdiction.
(2) A minor who is present within this state at the time the petition for adoption is filed.
We first note that this statute is poorly worded. A minor does not have parental rights that may be terminated. Rather, her parents possess these rights. The legislature must have intended to state that a minor may be adopted if her "parents' rights have been terminated ...."
This court acknowledges that such an adoption may be prohibited by other provisions in the adoption statutes. However, this particular section should not be interpreted to allow this absurd result.
This holding obviously does not apply to stepparent adoptions. In a stepparent adoption, the minor is eligible to be adopted if the rights of one of her parents are terminated. Sec*510tion 48.81, Stats., does not clearly provide for this exception in the case of stepparent adoptions. However, it is clear from surrounding statutes that the legislature intended to sanction stepparent adoptions. See secs. 48.92(2) ("unless the birth parent is the spouse of the adoptive parent") and 48.835(3)(b) ("[i]f the person filing the adoption petition is a stepparent"). The same cannot be said for the proposed adoption in this case. No neighboring statutes indicate that the legislature intended to allow any adoptions, other than stepparent adoptions, unless the rights of both of the child's parents have been terminated.
Section 48.92, Stats., provides as follows:
48.92 Effect of adoption. (1) After the order of adoption is entered the relation of parent and child and all the rights, duties and other legal consequences of the natural relation of child and parent thereafter exists between the adopted person and the adoptive parents.
(2) After the order of adoption is entered the relationship of parent and child between the adopted person and the adoptive person's birth parents, unless the birth parent is the spouse of the adoptive parent, shall be completely altered and all the rights, duties and other legal consequences of the relationship shall cease to exist. Notwithstanding the extinction of all parental rights under this subsection, a court may order reasonable visitation under s. 48.925.
(3) Rights of inheritance by, from and through an adopted child are governed by s. 851.51.
(4) Nothing in this section shall be construed to abrogate the right of the department to make payments to adoptive families under s. 48.48 (12).
This case involves "[t]he adoption of an adopted person ... [and thus] the references to parent and birth parent [in the statutes] are to adoptive parent." See sec. 48.96, Stats.
The statute does exempt the birth parent from this "cutoff1 provision in stepparent adoptions. However, because Georgina and Annette are not married, this exception does not apply.
The petitioners cite to decisions from other states that have found similar "cut-off provisions are directory. See Adoption of B.L.V.B., 628 A.2d 1271 (Vt. 1993); Matter of Adoption of Evan, 583 N.Y.S.2d 997 (Sur. 1992). While this court may look to decisions from other jurisdictions when interpreting similar statutes, our primary purpose in interpreting a statute "is to determine the legislative intent and the policy behind the statute." State v. Hopkins, 168 Wis. 2d 802, 815, 484 N.W.2d 549 (1992). Although we take note of these decisions, they shed little light on the intent of the Wisconsin legislature.
In. pari materia refers to statutes relating to the same subject matter or having the same common purpose. Black's Law Dictionary 791. As a rule of statutory construction, in pari materia requires a court to read, apply and construe statutes relating to the same subject matter together. Id.
Amici curiae — the National Center for Lesbian Rights, Lambda Legal Defense and Education Fund, Inc., Gay and Lesbian Advocates and Defenders and the Northwest Women's Law Center — suggest that this court could view Annette's petition for adoption as a joint petition filed by Annette and Georgina subsequent to the termination of the parental rights of both Georgina and Terry. According to the amici, this alternate procedure would avoid the impediments to the proposed adoption presented by secs. 48.81 and 48.92, Stats. At oral argument, the petitioners also advanced this argument. The Supreme Court of Massachusetts recently affirmed an order of adoption based on a similar argument. Adoption of Tammy, 619 N.E.2d 315 (Mass. 1993).
The validity of a joint adoption is not before this court. Annette and Georgina did not jointly petition to adopt Angel. Only Annette filed such a petition. Furthermore, no one petitioned for the termination of Georgina's parental rights. Hence, this court will not address this alternate argument. We do note that this court has previously suggested that the validity of a joint adoption by two unmarried individuals is best left to the legislature. In re Interest of Z.J.H., 162 Wis. 2d 1002, 1019 n.11, 471 N.W.2d 202 (1991). Presently, sec. 48.82, Stats., allows adoption only by a single adult, a married couple or the stepparent of the child.