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.