In discussing the issue of wholes and parts, we must distinguish between pre-theoretical and theoretical conceptions. Consider, for comparison, a similar distinction that might be drawn in discussing the nature of heat. We have, on the one hand, a pre-theoretical understanding of the notion of heat, an understanding which determines the appropriate use of the term "hot". On the other hand, we have theoretical proposals which are intended to explain what the property is hot consists in, such as, for example, the (no longer plausible) proposal that it consists in the presence of a type of material substance known as "caloric", or the alternative proposal that it consists in the molecules making up the hot thing being in such a state as to possess a mean kinetic energy of higher degree than some specified standard. Some of the main tasks of a study of the nature of heat are the introduction and development of, and decision between, such alternative proposals.