Value in economics refers to a measure of economic worth as determined by the market. Definitions vary as to how to calculate and define value. For example, neoclassical economists see the value of an object as simply the price it would bring in an open and competitive market. Classical economists, on the other hand, see the value of an object as the amount of discomfort or labor saved through the consumption or use of an object or condition. Supply and demand dictate the value of an object, and the price of an object is often called its exchange value. As a symbolic representation for the cost as determined by economic sources or forces, value is often connected to the labor that produces the product, in addition to the product itself. Theories of value explain the varying market forces that guide the construction of value as predicted by models. When measured in monetary terms, value is most often positive in magnitude because market forces dictate a cost for an object that is non-negative. Value can be negative, however, but for that to be true the unit of analysis would have to be something other than money.