By Joseph Loy and Justin Bova ( November 27, 2017, 9:53 AM EST) -- If you were to ask for a description of a pencil, you might hear of its color, shape and size, and that it consists of graphite and wood or plastic. You might also hear of its application: People use pencils to write and draw on paper. Indeed, most articles or systems involve practical applications, so it is tempting to describe them both in terms of what they are and what they do. Expedient or effective as it may be, describing a system and the method of using it carries risk in patent drafting because patent claims are restricted to a single category of invention. When patentees blend categories, such as a system and a method, they risk indefiniteness for "mixing claims." In other words, although a single patent may include different claim types, a single patent claim may not mix elements of a system and a method without risking invalidity for indefiniteness....