The government doesn't own it, but it enforces the right that you own it. Both for physical goods in the obvious way, and IP via the way of copyright.
We now live in a world where the machines needed to copy things are commonly owned by individuals. Copyright, having been designed to regulate industry, is massively out of date -- individuals do not have the resources needed to decide if they are abiding by copyright. Even the entertainment companies that cry about the importance of copyrights know this, which is why they keep pushing for DRM. No sane person actually believes that normal people are going to stop and think about whether or not they are obeying copyright laws; that is just not how people generally behave.
The truth is, in the 21st century copyright is nothing more than a red flag law that exists solely to protect obsolete industries.
So what? The previous poster's point is that both forms of property are social contracts. All private property, physical or otherwise, are nothing but societal agreements, regardless of whether there is a written record or what point in history the agreement began.
What people have in the absence of government is not property, but merely possession. No more or less binding on anyone else than a dog with a bone.
You have to wonder if the framers talked about our actual natural rights in such disrespectful terms: "The saying there shall be no monopolies lessens the incitement to ingenuity, which is spurred on by the hope of a monopoly for a limited time, as of 14 years; but the benefit even of limited monopolies is too doubtful to be opposed to that of their general suppression."
Does this strike you as being even remotely analogous to the situation faced by the people who make television, movies, books, and music?
The same goes for any other form of permissions. If I get a government permission to sell drugs or produce weapons, I would not call that a property right, comparable to the car I own. The permission to enter a house is not comparable to the property right of the person who owns the house.
If we look at copyright specific, it is an intrusion into the property right of others. Its not just a permissions, but also a restrictions of the actually property owners rights. By calling copyright a property equal to physical objects, we are making the term property meaningless to the point of contradiction.