What are the three main requirements under 112(a) for patent applications?

The three main requirements under 112(a) of the United States patent law are indeed the written description, enablement, and best mode.

The written description requirement mandates that the patent application clearly conveys that the inventor has possession of the invention at the time of filing. This means that the description must adequately detail the invention so that someone skilled in the field can understand what is being claimed.

Enablement requires that the application provides enough information for a person skilled in the art to make and use the invention without undue experimentation. This ensures that the patent is not granted for ideas that are not fully developed and cannot be replicated by others in the field.

The best mode requirement states that the inventor must disclose the preferred method of carrying out the invention if such a method exists. This ensures that the patent covers not only the invention in general but also the best way to utilize it, thus promoting the sharing of knowledge within the field.

Together, these requirements help to ensure that patents are fully informative and accessible to those who may wish to build upon the inventor's work, while also providing adequate protection for the inventor's innovations.