How does the USPTO handle predictable versus unpredictable arts in written description evaluations?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

The USPTO’s approach to evaluating written descriptions differs between predictable and unpredictable arts. According to MPEP 2163.02:

“The level of detail required to satisfy the written description requirement varies depending on the nature and scope of the claims and on the complexity and predictability of the relevant technology.”

In predictable arts (e.g., mechanical or electrical inventions), less detail may be required in the written description because a skilled artisan can often envision the structure of an invention from brief descriptions or simple drawings. However, in unpredictable arts (e.g., biotechnology or chemistry), more detailed descriptions are typically necessary to meet the written description requirement. This is because the results in these fields are often less predictable, and a skilled artisan may not be able to readily envision the invention from a general description.

Examiners are instructed to consider the predictability of the art when determining whether the written description requirement has been met. In unpredictable arts, applicants may need to provide more experimental data or detailed explanations to demonstrate possession of the invention.