In this paper, we defend two claims. First, we argue that a notion of contextuality that has been formalized in physics and psychology is applicable to linguistic contexts. Second, we propose that this formal apparatus is philosophically significant for the epistemology of language because it imposes homogeneous rational constraints on speakers. We propose a Contextuality Principle that explains and articulates these two claims. This principle states that speakers update contextual information by significantly reducing the space of probabilities and variables in (...) a non-commutative way. Some contexts affect other contexts not merely in terms of the information they contain, but also on the basis of their sequential order. In particular, we argue that the Contextuality by Default theory provides a formalism that helps explain the role of contextuality in rational linguistic exchanges. (shrink)