Semantic and syntactic change of equis in Mexican Spanish

In this paper, we investigate the synchrony and diachrony of the linguistic item equis
in Mexican Spanish. Its original use is the letter x which stands for some variable
x. One function that appeared very recently is the discourse function according to
which equis is used to refer to some utterance from the discourse which denotes a
proposition and the speaker expresses his indifference whether this proposition is
true or not, e.g. A: Es verdad. ‘It’s true.’ B: Equis! ‘I don’t care (whether it is true or
not)’.
We analyze the diachronic change of equis from a variable-use x into a discourse
adverb as a shift of indifference over identities of entities into indifference over answers
to questions under discussion. This semantic shift is syntactically expressed
as a shift from nominal modifier into sentence modifier. We will argue that indifference
is pragmatically derived in the case of variable use and is lexically encoded
in the discourse use.