The controversy over the legalization of homosexual marriage is largely dependent on how natural law is interpreted. Both advocates and adversaries for homosexual marriage use natural law as a source of support for their arguments. There, however, seems to be a discrepancy between whether homosexuals violate natural law or exhibit natural law.
As its name would suggest, natural law is based on human nature. Nobody creates a natural law; rather, it is inherent in human behavior and therefore dictates our actions. The main principle of natural law is that good is to be encouraged and evil is to be avoided. (Aquinas, Q. 94) And since it is in human nature to be rational, humans are able to determine what is morally right or wrong. Natural law is especially ambiguous in comparison to positive laws because it is a concept that is assumed by our mere existence. Its openness to interpretation creates for contention in cases such as homosexual marriage.
A primary argument against homosexual marriage is its violation of natural law. Human beings are not naturally supposed to mate with the same sex, and therefore same-sex marriage is morally wrong. Furthermore, humans’ (and all living species, for that matter) main goal in life is to reproduce and create the best possible chance of survival for their offspring. Homosexual marriage defies this natural tendency to procreate, thus proving its unnatural tendencies. Opponents of same-sex marriage could also argue that the act would go against the interests of the common good since a majority of people is against the idea. According to Thomas Aquinas, the moral purpose of law is to order human affairs for the common good (Q. 90). Same-sex marriage, it would then appear, is immoral on this count.
The same natural law that is used to criticize homosexual marriage can also be used to support it. If it were unnatural for man to be homosexual, then nature would not even create homosexual men. These men would naturally be attracted to the opposite sex, but they are not. Proponents of same-sex marriage argue that it is, in fact, natural for some humans to be homosexual. Their genetic makeup, something they are naturally born with, may be the cause of their homosexuality. And although they may not physically be able to procreate, it does not necessarily mean they do not have the inherent want to reproduce. Furthermore, proponents for same-sex marriage could argue against the notion that permitting it would go against the common good. They could instead say that it is actually promoting the common good by maximizing happiness for those who want same-sex marriage the most.
Because natural law does not explicitly permit or reject same-sex marriage, its strength in this contention is diminished. In my opinion, neither position can use natural law as its only argument. The ambiguity of this law, furthermore, reflects the ambiguity of all law. The same way that natural law can be interpreted in a multitude of ways, so can other kinds of law. Since humans create positive law as a result of their rational nature, perhaps natural law’s ambiguity is projected onto all law that is man made.