The scope of a trademark is determined by whether there is "likelihood of confusion" (note that this is different from whether there has been any actual confusion), between that trademark and another trademark in the minds of the consuming public. Likelihood of confusion is generally determined by reviewing a set list of factors which, depending on the judicial circuit, range from 7 to 13 in number. In the Federal Circuit, for example, these are called the DuPont factors:
We determine likelihood of confusion by focusing on the question whether the purchasing public would mistakenly assume that the applicant's goods originate from the same source as, or are associated with, the goods in the cited registrations. [citation]. We make that determination on a case-by-case basis, [citation], aided by the application of the factors set out in In re E.I. du Pont de Nemours & Co., 476 F.2d 1357, 177 USPQ 563 (CCPA 1973). Those factors are:
1. The similarity or dissimilarity of the marks in their entireties as to appearance, sound, connotation, and commercial impression.
2. The similarity or dissimilarity and nature of the goods . . . described in an application or registration or in connection with which a prior mark is in use.
3. The similarity or dissimilarity of established, likely-to-continue trade channels.
4. The conditions under which and buyers to whom sales are made, i.e. "impulse" vs. careful, sophisticated purchasing.
5. The fame of the prior mark.
6. The number and nature of similar marks in use on similar goods.
7. The nature and extent of any actual confusion.
8. The length of time during and the conditions under which there has been concurrent use without evidence of actual confusion.
9. The variety of goods on which a mark is or is not used.
10. The market interface between the applicant and the owner of a prior mark.
11. The extent to which applicant has a right to exclude others from use of its mark on its goods.
12. The extent of potential confusion.
13. Any other established fact probative of the effect of use.
Id. at 1361, 177 USPQ at 567. Not all of the DuPont factors may be relevant or of equal weight in a given case, and "any one of the factors may control a particular case," In re Dixie Rests., Inc., 105 F.3d 1405, 1406-07, 41 USPQ2d 1531, 1533 (Fed. Cir. 1997).
(from In re Majestic Distilling Co. (Fed. Cir. Jan. 2, 2003)