Supporters of Minnesota's proposed marriage amendment are exactly right about something: Marriage is an important and valuable institution.

However, by seeking to amend the state Constitution rather than relying on the statute that already bars same-sex marriages, they unnecessarily imperil another important and valuable institution: the tradition of constitutional governance, in which a constitution serves to protect (not limit) individual freedoms through the division of governmental powers, the creation of checks and balances, and the specific provision of individual rights.

It does matter that what the marriage amendment proposes to change is Minnesota's Constitution rather than a statute. In the American tradition, we carefully distinguish a Constitution from a statute: A statute often restricts the freedom of individuals (for example, by defining something as a criminal act), while a constitution structures the government and purposefully limits its ability to abridge the freedom of citizens. Unlike a statute, a constitution serves to protect and increase individual freedom, not to limit it.

Our best example of this bedrock principle is the work of those who wrote the United States Constitution and Bill of Rights -- courageous and inspired men who crafted the central document in our society. Their discussion and writing was marked by a profound belief in individual freedom and a distrust of government's tendency to put limits on that freedom.

At the heart of their genius was a radical parsimony, and they were careful to ensure that the federal Constitution enumerated individual freedoms rather than limitations on freedom; such limitations were to be dealt with through statutes. The marriage amendment runs counter to this simple and settled American ideal.

Minnesotans have historically and enthusiastically supported this role for a constitution. It should be no surprise that the first article of our state Constitution tracks the ideals and even the language of the U.S. Bill of Rights. Nor was that understanding lost over the years. Since the adoption of the Minnesota Constitution in 1857, amendments have almost universally done one of three things: Structure government, fund various projects, and expand (not limit) individual freedoms. Defining limits on marriage simply does not fit.

There is a very important sense in which the marriage amendment is anything but "conservative": It rejects a longstanding and fundamental understanding of the function of a constitution that reaches hundreds of years into our history. While in one sense amendment proponents seek to preserve our heritage, in another and important sense they seek to destroy it. In their zeal to define marriage, social conservatives have run up against a conservative principle we should all care about -- that the Minnesota Constitution should limit government, not the freedom of individuals.

Amendment proponents are concerned that "activist judges" might overturn the law that currently defines marriage, but that is true of all statutes, and it is no reason to upend the core purpose of a constitution. Many criminal statutes, for example, have been found unconstitutional, but we would not want to simply paste the criminal law into our state Constitution to solve that problem.

As for the men who wrote the federal Constitution-- would they have approved of gay marriage itself? Probably not, but they would not have put that disapproval in the Constitution; they understood the purpose of the document that they were writing. It's for that reason that they did not include in the U.S. Constitution a ban on mixed-race marriages, which was a very real issue at that time. Such social rules were understood to be, and were, the province of statutes, not of the Constitution.

Americans of all political views revere the collective intellect that created our longstanding democracy. Part of what those men did was decide, crucially, that the U.S. Constitution needed to protect against an overreaching government, rather than dictate social policy. We are not wiser than they, and should not pretend such wisdom by putting an express limit to individual freedom into our state Constitution.

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Mark Osler is a professor of law at the University of St. Thomas.