At the Echo Nest, a “music intelligence” company owned by Spotify, a software engineer named Glenn McDonald has created a sprawling map of musical genres called “Every Noise at Once.” At last count, he had identified more than 1,400 genres — including those old favorites “future garage” and “symphonic black metal.”

Even though a computer might struggle to see a strong difference between two forms of music, humans seem intent on finding one. As an example of two genres where the music sounds quite alike but isn’t, Mr. McDonald cites “vegan straight edge” versus “hatecore.” If you didn’t know the categories, you might have trouble telling them apart — but meet the two groups of fans and the difference would be pretty apparent.

This also tells us that, very often, these distinctions are for social purposes: People label music, music labels people. As with the rainbow, a country song and a rock song might be musically closer than two songs within either genre, but in our minds, the genre threshold takes precedence.

Categorization affects not just how we perceive things, but how we feel about them. When we like something, we seem to want to break it down into further categories, away from the so-called basic level. Birders do not just see “birds,” gardeners do not just see “flowers”; they see specific variations. The more we like something, the more we like to categorize it.

As the psychology professor Debra Zellner has found, people who put drinks like coffee or beer into particular categories actually liked the everyday beverages more than the people who simply labeled everything as undifferentiated “beer” or “coffee.” Thus one online reviewer at the site BeerAdvocate described a brew as a “perfect lawn mower beer.” Is it the best beer ever? No. Is it good enough on a hot day after sweaty yardwork? Absolutely.

These connoisseurs experienced less “hedonic contrast” — the “lawn mower” beer might suffer by comparison with a Belgian saison, but rise in a drinker’s estimation if it were simply lumped with other beers of its type.

When we struggle to categorize something, we like it less. In a study recently published in the journal PLOS One, the subjects were shown a variety of “gender-ambiguous” morphed images of men and women.