A thing is anything that can be distinguished from everything else. If you can point at it, name it, or talk about it, it is a thing. A rock is a thing. A color is a thing. A number, a feeling, a country, a mistake — all things. “Thing” is the most general word there is. Everything in this library is a thing.

A thing has qualities — properties that make it distinguishable. A red ball is distinguished from a blue ball by color. A heavy box is distinguished from a light box by weight. Without at least one quality, there is nothing to distinguish, and so nothing to call a thing.

Things can be physical or not. A chair is a physical thing — it has mass, takes up space, you can sit on it. A promise is a non-physical thing — it exists, it matters, it can be broken, but it has no weight. Both are things. The word makes no commitment about physicality.

Things can contain other things. A box contains books. A room contains furniture. A country contains cities. Containment is one of the most basic relations between things — see container.

Things can be parts of other things. A wheel is part of a car. A chapter is part of a book. A cell is part of an organism. Parthood is different from containment — the wheel IS part of the car, but a book inside a box is NOT part of the box.

In TAB (Things with Attributes and Behaviors), a thing is the base model from which all other models derive. A thing has a name and grammar (how to refer to it in language). An object is a thing with mass and notability. A container is a thing with contents. A person is a thing that can move and act. Everything starts from thing.