Though the notion of 'variables' have been used by mathematicians over centuries, the term 'function' was first introduced by Leibnitz. He treated various geometric quantities associated with a curve, like tangents, normals, etc., being 'functions' of the curve. The term 'function' was taken over by the Bernoulli and gradually the function concept lost its geometric character. Johann Bernoulli later defined it as follows: " A function of a variable quantity is a quantity composed in some way or other of this variable quantity and constants". Euler in 1748 gave the following definition of a function: "Every analytic expression, in which apart from a variable quantity all quantities that compose this expression are constants, is a function."
1646 - 1716