Spoken words depend on their linguistic context to be identified in fluent speech. We examined whether contextual dependence varied with the level of information conveyed by a word. In particular, we compared the intelligibility of closed-class vs. open-class words and of given vs. new discourse information. If speakers articulate most clearly words that provide the greatest information, then open-class words and new discourse information should be less dependent on context. Words were excised from conversational speech and presented to listeners for identification. Closed-class words were accurately identified significantly less often than open-class words and open-class words expressing given information were identified significantly less often than those expressing new information. Results can be attributed to the clarity of articulation of each segment in a word rather than to greater coarticulation between word boundaries for the less informative words. Furthermore, results cannot be attributed solely to focal stress. The results are interpreted as driven by a speaker's notions about what is functionally communicative.