Defining terms is important, but defining sets much less so. Arguments about "is X a Y?" often have little to no value in the abstract. There are exceptions,

Defining terms is important, but defining sets much less so. Arguments about "is X a Y?" often have little to no value in the abstract. There are exceptions, but these are when the definitions are the most precise and can be evaluated objectively. E.g., a square is a (type of) rectangle and therefore its area is length * width. As the article shows, "is a whale a fish" has no value in the abstract. It depends on if you want to hunt it or know about its evolutionary path. Is a tomato a fruit or a vegetable? It depends on if you are a chef or a botanist. The botanists have the more rigorous definition, but I wouldn't call the chefs wrong. What about a pumpkin? Is a strawberry a berry? (https://imgur.com/gallery/pfEnXNT https://imgur.com/gallery/pfEnXNT) You probably saw the memes go around a while back about what is a sandwich, according to D&D alignments. Good for a laugh and a debate. But let's say you settle the question "is a hotdog a sandwich?" Now what? What did you get from that effort? It doesn't tell you anything about a hotdog that you didn't already know.