"Likelihood of confusion" is the heart of trademark law — the test for both USPTO refusals and infringement lawsuits. It comes from a 1973 case, In re E.I. du Pont, which laid out thirteen factors. In practice, a handful do most of the work.
The factors that usually decide it
- Similarity of the marks — in appearance, sound, connotation, and overall commercial impression. Note "sound": Kwik and Quick collide even though they're spelled differently. This is why phonetic searching matters.
- Relatedness of the goods/services — do they travel together in the marketplace? Identical marks can coexist in unrelated fields (Delta the airline vs. Delta the faucet).
- Similarity of trade channels — same stores, same buyers, same websites?
The supporting cast
Conditions of purchase (a $2 impulse buy invites more confusion than a $50,000 considered one), the fame of the earlier mark (famous marks get a wider berth), the number of similar marks already coexisting in a crowded field, evidence of actual confusion, and how long the two have coexisted without problems.
How to think about your own name
Don't just ask "is this exact name taken?" Ask: does anything sound like it, mean the same thing, or read the same way — for goods a buyer might think come from the same source? That reframing is the whole game, and it's what a real clearance search evaluates. A near-identical mark in a totally unrelated industry is often fine; a loosely similar mark in your exact lane can be fatal.