There are no ideologically 'neutral' sign systems: signs function to persuade as well as to refer. Modern semiotic theory is often allied with a Marxist approach which stresses the role of ideology. Ideology constructs people as subjects through the operation of codes. According to the theory of textual positioning, understanding the meaning of a text involves taking on an appropriate ideological identity (see 'Ideal readers'). For Althusser, ideology was a system of representation involving 'transparent myths' which functioned to induce in the subject an 'imaginary' relation to the 'real' conditions of existence.