For example, the young child, after observing that things like milk, water, and maple syrup are different in kind from things like tables and walls, arrives at the concepts of "liquid" and "solid." Forming the concept "liquid" involves a combination of isolation, abstraction, and integration. One must mentally isolate milk, water, syrup, and so on from solid objects and then must unite them into a single concept on the basis of their attribute of "liquid-ness," abstracted from all the other characteristics of liquids such as specific volumes, viscosities, and densities.