The world of patents and intellectual property is shifting more and more towards intangibles and ideas and away from concrete products, and current structures may not be able to cope, according to Federal Reserve chief Alan Greenspan.
Greenspan: Time to rethink intellectual property?
"Are the protections sufficiently broad so as to encourage innovation, but not so broad as to shut down follow-on innovation?" Mr Greenspan asked his audience at a conference in Georgia via a satellite video link.
Recent years have seen thousands of patents for "business processes" which often result in lengthy lawsuits as different companies fight over who gets royalties and who has to pay them.
In one instance, UK telecoms giant BT tried to suggest it had a patent on the "hyperlink" - the basic building block of the entire web - before a US court threw out its claim.
And a massive row is still under way over patenting genes, given that they are only being discovered, not invented.
Mr Greenspan made no judgements over whether the rules designed to cope with real-world, concrete property were too tight or too loose to make sure protection for ideas contributed to economic growth.
Nor did he comment on the Fed's economic policies or the state of the US economy.
But he made it clear that hard decisions and deep thinking was needed to make sure that the balance was right.
"Ownership of physical property is capable of being defended by police, the militia or private mercenaries," he said.
"Ownership of ideas is far less easily protected."
One ancient example, he commented, was that of calculus, the mathematical tool discovered by Gottfried Leibniz and Sir Isaac Newton in the 17th century, noting that their discovery was made freely available, triggering massive intellectual advances elsewhere.
Should we have protected their claim in the same way that we do for the owners of land?" he asked.
"Or should the law make their insights more freely available to those who would build on them, with the aim of maximising the wealth of the society as a whole? Are all property rights inalienable, or must they conform to a reality that conditions them?"