Why do humans have linguistic intuition?

People have spontaneous intuitions about sentence acceptability. These intuitions are critical for the scientific study of language and cognition yet we have little understanding of why humans have them in the first place. What is it about human minds that causes some sentences or utterances to trigger a psychological sense of oddness? The prevailing assumption is that we have some intuitive sense of what is grammatical and what is not. Here I present an alternative approach grounded in theoretical and empirical knowledge from cognitive linguistics, cognitive psychology and evolutionary psychology. Sentences are unacceptable when, and only when, there appears to be an intrinsic impossibility of interpreting them in any way consistent with the unconscious presumption of optimal relevance that underpins the interpretation of all stimuli perceived as communicative. This hypothesis explains why linguistic intuitions track grammaticality; it identifies how linguistic intuitions relate to visual illusions; it shows the merits of theoretical synthesis across traditional boundaries; it aligns with evolutionary perspectives to the mind; and it implies that there may be no particular cognitive capacity that functions to distinguish the grammatical from the ungrammatical. Linguistic intuitions are rather byproduct effects of core cognitive capacities for the interpretation of communicative stimuli.