# Why does the profit function in standard neoclassical theory have exactly one maximum?

In neoclassical theory is said that the highest profit occurs when Marginal Cost equals Marginal Revenue, but this condition wouldn't be enough to determine the maximum if there were more than one. The fact that the maximum can be determined like this means that the uniqueness of the maximum derives from the assumptions of the theory? My professor said that the uniqueness is determined by the static nature of the theory, but this seems to me a little vague. How can it be explained in a more satisfactory way?