"A major advance in notation with far-reaching consequences was François Viète's idea, put forward in his "Introduction to the Analytic Art"... of designating by letters all quantities, known or unknown, occurring in a problem. ...for the first time it was possible to replace various numerical examples by a single "generic" example, from which all others could be deduced by assigning values to the letters. ...by using symbols as his primary means of expression and showing how to calculate with those symbols, Viète initiated a completely formal treatment of algebraic expressions, which he called logistice speciosa (as opposed to logistice numerosa, which deals with numbers). This "symbolic logistic" gave some substance, some legitimacy to algebraic calculations, which allowed Viète to free himself from the geometric diagrams used... as justifications."