What does the transitional phrase "consisting essentially of" do in a patent claim?

The phrase "consisting essentially of" in a patent claim serves as a transitional term that indicates the claim includes the specified materials or steps, but allows for the inclusion of additional unrecited elements that do not materially affect the basic characteristics of the invention. This means that while the claim identifies certain essential components or steps, it permits certain variations or additional features that can enhance the invention without changing its fundamental nature.

This transitional phrase strikes a balance between specificity and flexibility. For instance, if a claim for a composition includes several specified ingredients, the phrase allows for the addition of further ingredients as long as they do not alter the claimed invention's primary characteristics. This can be particularly valuable in fields like chemistry or material science, where minor modifications might not detract from the core inventive concept.

In contrast, other options suggest limiting or broadening the scope to an extent that does not accurately reflect the function of the phrase. Thus, "consisting essentially of" specifically serves to provide essential components while allowing for supplementary elements that maintain the basic nature of what is being claimed.