There are four states in which matter can exist: solid, liquid, gas, and plasma. Similarly, in an April Fools’ Day paper in 2022, Harvard’s Madelyn Leembruggen and Caroline Martin proposed that foods can be classified as soup, salad, or sandwich:

• “Soups are a suspension of ingredients in a liquid matrix, whereas salads are a suspension of ingredients in a gaseous matrix.” Thus cereal is soup, and mixed nuts are salad. The transition between phases is continuous: Depending on how finely they’re chopped, the same set of ingredients might produce a chunky salad, a salsa, or a gazpacho. Vanilla ice cream is a “glassy” soup because it doesn’t flow at its serving temperature, but it takes on a more liquid character as it melts.
• A soup or salad becomes a sandwich when it’s enclosed in a carbohydrate. The shape and quality of the carbohydrate must vary according to the substance it encloses, but a proposed general rule is that if you can pick up a dish by the carb and eat it, it’s a sandwich.

Further investigation is needed into some edge cases (e.g., lasagna vs. baked ziti), but in most cases a lot of ground can be covered by just asking “Is this a soup, a salad, or a sandwich?” “Most of the time, the answer you blurt out with the least amount of thought is the most true.”

“Finally, to remove any of the reader’s lingering uncertainty: yes, a hotdog is a sandwich.”

(Madelyn Leembruggen and Caroline Martin, “What’s for Lunch? A Systematic Ordering of Foods in the Soup-Salad-Sandwich Phase Space,” arXiv preprint arXiv:2203.16580 [2022].)