The scientific study of the properties of signaling systems, whether natural or artificial. In its oldest sense, it refers to the study within philosophy of sign and symbol systems in general. In this approach, linguistic, psychological, philosophical and sociological characteristics of communicative systems are studied together. The philosophers Charles Peirce (1834-1914), Charles Morris (1901-1979) and later Rudolf Carnap (1891-1970) saw the field as divisible into three areas: semantics, the study of the relations between linguistic expression and the objects in the world which they refer to or describe; syntactics, the study of the relation of these expressions to each other; and pragmatics, the study of the dependence of the meaning of these expressions on their users (including the social situation in which they are used). In the second part of the twentieth century, the term ‘semiotics’ came to be applied to the analysis of pattered human communication in all its sensory modes, i.e. hearing, sight, taste, touch and smell. The branch of the subject which has received most study is the vocal-auditory mode, primary through the subjects of phonetics and linguistics.