The similarity or dissimilarity of the marks in their entireties as to "appearance, sound, connotation and commercial impression" is often a “predominant” or “fundamental” inquiry in the likelihood of confusion analysis. Herbko Int'l, Inc. v. Kappa Books, Inc., 308 F.3d 1156, 1165 (Fed. Cir. 2002); In re i.am.symbolic, llc, 866 F.3d 1315, 1324 (Fed. Cir. 2017); Federated Foods, Inc. v. Fort Howard Paper Co., 544 F.2d 1098, 1103 (CCPA 1976).

Similarity in all aspects is not required, such that similarity in spelling or sound alone could be a basis to find a likelihood to cause confusion.” Krim-Ko Corp. v. Coca-Cola Bottling Co., 390 F.2d 728, 732 (CCPA 1968) (citation omitted); see also Hancock v. Am. Steel & Wire Co., 203 F.2d 737, 740 (CCPA 1953) (“it is proper to consider [the marks'] appearance, sound and meaning … but a combination of all three factors need not necessarily exist”) (cleaned up; citations omitted). And where a trademark is not a recognized word, evidence suggesting that potential consumers would pronounce the mark in a particular way should not be ignored. StonCor Grp., Inc. v. Specialty Coatings, Inc., 759 F.3d 1327, 1331-32 (Fed. Cir. 2014). 

Furthermore, because people usually are exposed to marks at “spaced intervals,” Grandpa Pidgeon's of Mo., Inc. v. Borgsmiller, 477 F.2d 586, 587 (CCPA 1973), they “ordinarily must depend upon their past recollection” when later exposed to a similar mark. Franklin Mint Corp. v. Master Mfg. Co., 667 F.2d 1005, 1007 (CCPA 1981). So, rather than a “side-by-side comparison,” marks are considered “in light of the fallibility of memory.” In re St. Helena Hosp., 774 F.3d 747, 751 (Fed. Cir. 2014) (citation omitted); see also Diamond Alkali Co. v. Dundee Cement Co., 343 F.2d 781, 784 (CCPA 1965) (the test is whether confusion is likely when “the marks are compared by separate recall later in time and removed in place”).

“The proper test is … whether the marks are sufficiently similar in terms of their commercial impression such that persons who encounter the marks would be likely to assume a connection between the parties.” i.am.symbolic, 866 F.3d at 1323 (citation omitted); see also Phillips Petroleum Co. v. Knox Indus. Corp., 277 F.2d 945, 947 (CCPA 1960) (“The issue is whether the marks are confusingly similar, not whether they are identical.”) (citation omitted). 

For example, in St. Helena Hosp., 774 F.3d at 750-51, the TTAB considered TAKETEN and TAKE 10! and held that “the differences in appearance are minimal.”

In Contour Chair-Lounge Co. v. Englander Co., 324 F.2d 186, 189 (CCPA 1963), finding “‘Contur' but a slight misspelling of ‘Contour,'” the Court held that confusion was likely as between CONTURFOAM for mattresses and box springs and CONTOUR for chairs.

In National Mineral Co. v. Norwich Pharmacal Co., 183 F.2d 119, 120 (CCPA 1950): “That the marks [Swav and Suave] are alike in meaning we think is clear, both indicating smoothness, sleekness and good grooming. Therefore, as far as the similarity between the marks is concerned, we deem that in sound and meaning they are not, in a trade-mark registration sense, legally distinguishable.”

More recently, the TTAB concluded that consumers will perceive DIRDYBIRD simply as a slight misspelling of DIRTYBIRD. In re RZT LLC, Ser. No. 98913556 (TTAB Oct. 2, 2026). Applicant argued that its DIRDYBIRD mark “connotes the feeling of a bird that is sturdy … .” The TTAB was not persuaded, noting that the mark was not STIRDYBIRD or STURDYBIRD.