The various non-legal meanings of the concept of certainty are discussed, starting with the meaning of the word "certainty" as often used to refer to a sense of external, physical, or objective security. Next is certainty in the sense of trust (in psychology, economics, philosophy, and political science), and protection of individual or collective goods. These definitions are used to differentiate simple certainty from legal certainty properly speaking. The goal is to demonstrate that legal certainty takes on importance only when it transcends the individual psychological dimension and enters the socio-axiological (but not merely behavioral) dimension: thus legal certainty represents certainty as an intersubjective value event associated with the law of a given society, either as a norm or as a value, and with the legal universe as its object or instrument.