The fair price also called right value is a theoretical and virtual notion nearer of the value (= estimate) that Prix (= of market). It was advanced by Thomas d' Aquin in his Summa Theologica .

The fair price would be, according to the approaches:

• the potential price estimated starting from elements considered objective (cost, utility, scarcity, etc),
• a substitute of the contract price when there does not exist Marché organized giving a reliable reference on the equilibrium price between supply and;
• the desirable price according to appreciations considered ethical;
• a meaningless word.

For the financial credits, concerning the relation between the fair price and the price contract, there are two approaches:

• the assumption of Efficiency of the market which considers that both agree;
• and the behavioral Finance which notes variations being able to be important and durable between the two.