of language and speech, however, concepts (the signified part of the sign), are likewise founded on social contract. To explain how the social solidification of language comes about, Saussure proposes the notion of individual speaking. Speaking is willful and intentional. While individual speaking is heterogeneous, that is to say composed of unrelated or differing parts or elements (relating to 'external' or interdisciplinary linguistics), language is homogeneousa system of signs composed of the union of meanings and "sound images". Therefore, as the core of linguistic inquiry can be isolated focusing on the self-contained, non-physiological system of signs, which Saussure calls language, it is this that general linguistics focuses on since it allows an investigative methodology that is "scientific" in the sense of systematic inquiry. General linguistics is also analogous with biology to the extent that linguistic forms—like organisms—are analyzed anatomically (as in morphology). In practice, Saussure proposes that general linguistics consists of the analysis of language itself by way of semantics, phonology, morphology, lexicology, and grammar. Moreover, general or internal linguistics is informed by the related disciplines of external linguistics such as anthropological and archaeological linguistics. While language is the ultimate object of research, it must be studied through speech, which provides the research material. For practical reasons, linguists mostly use texts to analyse speech to uncover the systemic properties of language. The sign The focus of Saussure's investigation is the linguistic unit or sign. The sign (signe) is described as a "double entity", made up of the signifier, or sound pattern (referred to by Saussure as a 'signal'), and the signified, or concept (referred to by Saussure as 'signification'). The sound pattern is a psychological, not a material concept, belonging to the system. Both components of the linguistic sign are inseparable. One way to appreciate this is to think of them as being like either side of a piece of paper – one side simply cannot exist without the other. The relationship between signifier and signified is, however, not quite that simple. Saussure is adamant that language cannot be considered a collection of names for a collection of objects (as it is in the conception that Adam named the animals, for example). According to Saussure, language is not a nomenclature. Indeed, the basic insight of Saussure's thought is that denotation, the reference to objects in some universe of discourse, is mediated by system-internal relations of difference. Arbitrariness For Saussure, there