Is 101 redundant?

In Bilski, the Supreme Court reiterated the “three specific exceptions” to the broad expanse of patentable subject matter defined by 35 USC 101: “laws of nature, physical phenomena, and abstract ideas.”  But are these exceptions necessary?

Laws of nature and physical phenomena necessarily anticipate themselves.  Gravity has billions of years of prior art behind it, for example.  Additionally, an inventorship issue arises with respect to natural things that are discovered; one could not patent X-rays, for example, solely on the basis of being the first to develop a detector to observe them.  (The detector, of course, would be patentable, and in this case almost certainly neither anticipated nor obvious.)  So, there is no need for an exception to 101 for these categories of subject matter.  Claims directed to that subject matter would fail fatally in the first Office Action.

An abstract idea, by definition, is not capable of enablement or reduction to practice, constructive or otherwise.  Thus, any claim directed to an abstract idea would lack description in the specification, and would be rejected under 112 during prosecution.

If 101 lets one patent anything that isn’t one of those three exceptions, but none of those three exceptions are needed to prevent claims directed to those three areas from issuing, then what’s it useful for?