11 Categories defined by Listing their Members

Many familiar and useful categories are defined in a simple way, just by listing the members of the category.   A sports team or a school homeroom class is defined this way — there’s a list of the people on the team or in the class.   A pro basketball player could be on any of the 30 NBA teams, and you could be in any of the homeroom classes for your grade.


Let’s consider the category of “United States.” There are 50 states in this category. An alphabetical listing of the United States starts with Alabama and Alaska and ends with Wisconsin and Wyoming. The state of California (abbreviation CA) is the tall and skinny state on the left side of the map where the United States reaches the Pacific Ocean.

Let’s make sure you understand why “United States” is a list category. We can define the category of “state” using property tests like “is it a geographical territory contained within a country?” and “does the territory have its own government?”  So we can test whether California is a state, but there is no test that determines whether it is one of the United States.

Now you should understand why “cleaning up your room” by hiding everything under the bed doesn’t organize your room very much.  You created a category of “things under the bed” — a list category.   The things under the bed don’t have any properties in common. There is no test for whether something should be under the bed or not.


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"The Discipline of Organizing" for Kids Copyright © 2022 by Robert J Glushko is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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