The overall purpose of trademark law is to avoid any consumer confusing the source of one product, with the source of another product. The Lanham Act prohibits the registration of use of a trademark if that mark is likely to cause confusion. In each application before the USPTO, the examining attorney must only consider the facts of the application in front of him. Prior trademark decisions and other products have little to no impact on the determination.
The USPTO emphasizes that usually, no single factor will determine whether consumers will be likely to be confused. The factors are looked at as a whole. Some factors may be given more or less weight than others in any given situation. The Trademark Trial and Appeal Board follow what is know as the “du Pont” factors when determining likelihood of confusion. The du Pont factors are: