Soup, stew and braise overlap, but the useful distinction is not the name of the pot. It is the proportion of liquid, the size of the ingredients and whether the cooking liquid is served as broth, thickened around the food or reduced into a sauce.
Soup is organised around the liquid
A soup may be clear, thick or puréed, but its liquid remains a principal part of each serving. The solids can be substantial; what matters is that the bowl is meant to be eaten with the broth rather than lifted out of it.
Stew keeps liquid close to the food
Stew usually uses smaller pieces and enough liquid to cook them together. Starch, collagen, purée or reduction may thicken that liquid until it coats the ingredients. The finished sauce is part of the dish, but it does not dominate the serving as soup broth does.
A braise treats larger pieces deliberately
A braise generally cooks a larger or intact main ingredient with relatively little liquid in a covered vessel. Browning may come first, then gentle cooking softens connective tissue or vegetable fibre. The food can be removed while the liquid is strained or reduced separately.
Names follow cuisines, not a laboratory
Many traditional dishes sit between these definitions, and translation makes the borders less exact. Use the terms to understand a recipe's mechanics, not to tell a cuisine what it is allowed to call its food.
