A common definition of temperature, as stated by one dictionary, is: “Degree of hotness or coldness measured on a definite scale based on some physical phenomenon (as the expansion of mercury in a thermometer).” However, to rigorously define the concept of temperature, one can use the idea of operationalism, which asserts that a concept is synonymous with a corresponding set of operations. Thus, “temperature” can be defined by the five operations needed to construct a temperature scale. There are many arbitrary decisions in doing this.