] In the case of physical property, we take it for granted
] that the ownership right should have the potential of
] persisting as long as the physical object itself. In the
] case of an idea, however, we have chosen to strike a
] different balance in recognition of the chaos that could
] follow from having to trace back all the thoughts
] implicit in one's current undertaking and pay a royalty
] to the originator of each one. So rather than adopting
] that obviously principled but unworkable approach, we
] have chosen instead to follow the lead of British common
] law and place time limits on intellectual property
] rights.

I'm rerecommending this. I've read it now. Greenspan explains the changing nature of the situation just as I have in the past, and this talk offers itself as a good reference for such an explanation, as people usually don't want to take my word for it. :)

Intellectual Property is broken. You heard it here from the guy that runs the economy. So don't tell me I'm being silly.

Of course, Greenspans perspective on how to fix it is probably 180 degrees from mine.

FRB: Speech, Greenspan-Market economies--April 4, 2003