It's the nation's oldest public park. It has been defended for nearly four hundred years from developers who would build on it, from massive crowds that would destroy it, from promoters who would create it into Winter Wonderland theme parks. It is a park for the people — not some people, but all people, regardless of their status, regardless of their ability to pay.

America is a young country with few spots that have been hallowed by the passage of time. But if there is any spot that is so hallowed, is so — dare one say? — sacred, it is the Common.

Now the city has moved to charge a fee for those who would use the Frog Pond, the newly renovated skating rink on the Common. The fee is wrong.

It's not wrong because the fee is high (at $3.00 for those 14 and over it's less than one would pay to skate at most other rinks in the area). It's not wrong because of some notion that skating should always be free.

It's wrong in principle. It's wrong because this city government has been entrusted with the care and maintenance of this space not just for this generation, but for all generations. Yet it has taken a series of well-intended actions, the consequences of which have been to convert a portion of this space from something that was public to something that is, quite decidedly, less so.

This notion of the Common as our most public of all public spaces seems to me sufficient to argue against imposing fees for those who would use it. Our responsibility is to keep this particular space as public as possible. We abdicate this responsibility by in effect privatizing part of that space.

There is a second concern with the fee as well: it blurs government's historic role of serving all, not just a few.

Government — the public sector — differs from the private sector in many respects. One clear difference is that it is the job of government to act in ways that private markets would not.

Private markets are terrific means of allocating goods and services to people on the basis of their willingness or ability to pay. Government historically has played a different role, providing services and goods to all, regardless of their ability to pay. Thus we have free libraries, free schools, police and fire protection for all and, yes, public parks.

The imposition of the user fees for the Frog Pond seems a subversion of this role. A user fee of $3 probably will not deter those of substantial means from skating on the Pond. But no one can deny that people of modest means inevitably will use it less frequently than they would if it were free.

We already have a number of skating rinks in the area, many of them privately owned, that charge a fee. The city spent millions of taxpayer dollars and corporate contributions to create the Frog Pond. Why do so if the end result is just another fee-based skating rink?

It's not a sufficient answer to assert that it costs money to run the Frog Pond. It also costs money to run the public library and the police department. What's next? A fifty cent fee every time one borrows a book from the Boston Public Library?

Of course not. These are precisely the kind of expenditures government should make for the benefit of everybody.

The rebuilding of the Frog Pond was a noble act, a symbol of Boston's renaissance as a city. It would be a shame if the Pond also became a symbol that this renaissance is for some, not all.