Now, in my view, to speak of “the purpose” of a statute is a confusion: statutes are cobbled together artificial legislative schemes, usually the result of many compromises. Congress has no “intent” or “purpose”; it’s composed of individual legislators who have their own motivations and purposes. A given legislator may have various purposes, including: rewarding special interest groups to increase the chance of campaign contributions, and so on. But we can hold a law up to its stated purpose, even if the real purposes of the legislators is different.
That there may be many subjective intents of legislators does not negate the presence of an objectively determinable functional analysis. The patent statute gives a right to exclude in return for disclosure. That's it.
Innovation produces a change in the way we live. Most patents don't yield innovation. Thus, it's hard to see the purpose of the patent system as one which incentivizes innovation. An issued patent gives an inventor a certain status in the marketplace. Innovation comes later.
***UPDATE. On 4 Jan 2012.
Relevant to the comment below and contrary to the assertion therein, IPBiz DID LINK to the Kinsella post containing the Kinsella quotation. Other than that, Kinsella's ramblings speak for themselves.
The functional outcome of US patent law is: in return for disclosing an enabled invention which is useful, new and not obvious, an applicant might get a right to exclude. That's all there is. The successful applicant, with the right to exclude, enters the marketplace and tries to make deals. Maybe the invention leads to innovation, maybe it does not. Most inventions do not change the way we live, so they are not properly termed innovations.
As to subjective intent of legislators, one doubts Congressman Waxman ever thought Hatch-Waxman would be used in the way it currently is, as to the six-month period of exclusivity.