This paper aims to explore the implications of the essentially contested nature of the concept of liberalism in the conceptualization of illiberalism in order to understand the existence of misunderstandings and contradictions in the delimitation and definition of the concept within illiberalism studies. To this end, we seek to show that the contributions of linguistic political theory, inspired by the work of Wittgenstein, are are to describe and understand the conflicts that illiberalism can raise. Indeed, since liberalism is both an ideology and an analytical concept, it is difficult to define the latter without arbitrating the ideological conflicts between the “liberals pretenders”. As the synoptic comparison of the genealogies of illiberalism found in the literature shows, these conflicts are transcribed in the conceptualization of illiberalism, in a more or less imperceptible way, and are sometimes instrumentalized to invert the function and content of the concept. Consequently, our hypothesis is that the notion of "grammar" is useful in clarifying the fact that the concept of illiberalism has a different function and purpose depending on what is considered liberalism and the liberal tradition, which ultimately allows us to assess the coherence and relevance of the concept's use.