Mind: A Brief Introduction (John R. Searle) / quote 70 of 138
Levels of description
Any complex system can be described in different ways. Thus, for example, a car engine can be characterized in terms of its molecular structure, in terms of its gross physical shape, in terms of its component parts, etc. It is tempting to describe this variability of descriptive possibilities in terms of the metaphor of “levels,” and this terminology has become generally accepted. We think of the microlevel of molecules as a lower level of description than the level of gross physical structure or physical components, which are higher levels of description. Most of the interest of this distinction is that it applies in a dramatic fashion to computers. At a lower level of description your computer and mine might be quite different. Yours may have a different type of processor than mine, for example. But at a higher level of description they may be implementing exactly the same algorithm. They may be carrying out the same program.