What type of invention is NOT directly patentable according to 35 U.S.C. § 101?

The correct answer is that abstract ideas are not directly patentable according to 35 U.S.C. § 101. This section defines the types of subject matter that can be patented, which include processes, machines, manufactures, and compositions of matter. However, abstract ideas fall outside the scope of what is considered patentable.

The rationale behind this is that abstract ideas are not tied to a specific application or practical implementation, making it difficult to show that they meet the requirements for patent eligibility, such as novelty and non-obviousness. The U.S. Patent and Trademark Office and courts have consistently held that abstract ideas must be woven into a practical application or accompanied by something more, such as a concrete implementation, to be eligible for patent protection.

In contrast, processes, machines, and compositions of matter are explicitly recognized as patentable subject matter under section 101, provided they meet the other requirements of patentability. This includes criteria such as being novel, useful, and sufficiently described. Thus, while specific processes, machines, and compositions of matter can be patented, abstract ideas cannot be directly patented unless they are applied in a tangible way that transforms them into eligible subject matter.