Human dialogue is governed by communicative norms that speakers are expected to follow in order to be viewed as cooperative dialogue partners. Accordingly, for language-capable autonomous agents to be effective human teammates they must be able to understand and generate language that complies with those norms. Moreover, these linguistic norms are highly context sensitive, requiring autonomous agents to be able to model the contextual factors that dictate when and how those norms are applied. In this work, we consider three key linguistic norms (directness, brevity, and politeness), and examine the extent to which adherence to these norms varies under changes to three key contextual factors (potential for harm, interlocutor authority, and time pressure). Our results, based on a human-subject study involving 5,642 human utterances, provide strong evidence that speakers do indeed vary their adherence to these norms under changes to these contextual factors.