The process in which something functions as a sign may be called '. This process, in a tradition which goes back to the Greeks, has commonly been regarded as involving three (or four) factors: that which acts as a sign, that which the sign refers to, and the effect on some interpreter in virtue of which the thing in question is a sign to that interpreter. These three components in semiosis may be called, respectively, the sign vehicle, the designatum, and the interpretant; the interpreter may be included as a fourth factor. These terms make explicit the factors left undesignated in the common statement that a sign refers to something for someone.