While speakers are theorized to ideally not include unnecessary information (redundancy) in their utterances, in reality, they often do so. One potential reason is that linguistic redundancy facilitates language communication, especially when the addressee (interlocutor) is linguistically less competent (e.g., an artificial system). In three experiments, we examined whether linguistic redundancy may arise as a result of people’s tendency to use similar linguistic features as their interlocutor does during communication (i.e., linguistic alignment) and whether redundancy alignment (if any) differs with a human interlocutor versus a computer interlocutor. We also examined whether redundancy alignment is affected by the perceived competency of the interlocutor, participants’ abilities in theory of mind (ToM), and if redundancy alignment varied across time during the experiment. Participants carried out a picture matching and naming task with a human or computer interlocutor who either always or never included redundancies in their utterances. Redundancy alignment was found across all experiments, in that speakers produced more redundancies with a redundant interlocutor compared to a non-redundant one. This alignment was also modulated by the perceived competency of the interlocutor, the time course of the interaction, and ToM abilities, suggesting that redundancy usage is affected by both automatic and strategic mechanisms of linguistic alignment.

An important quality to assess in others is their cooperativeness. We hypothesized that people use linguistic markers in their partners’ speech as a proxy of their cooperativeness in other tasks: specifically, we predicted that participants would prefer syntactically similar conversation partners as cooperation partners in a monetary game. We found that, indeed, participants preferably selected syntactically similar conversation partners as cooperation partners, but only when the participants could communicate using their naturally preferred constructions. In contrast, when participants were forced to communicate using dispreferred constructions, they rather cooperated with those partners that matched their natural preference than with those that matched their overt linguistic use. This pattern of results was likely driven by participants valuing representational alignment (i.e., being aligned on both linguistic features and their mental representations) more than incidental behavioral alignment (i.e., superficial convergence on similar linguistic features during interaction). This is because representational alignment is a potential indicator of group membership and may be associated with in-group benefits such as reputation, reciprocity and normative behavior. Those benefits may outweigh the benefits of simple behavioral alignment, which could be a potential indicator of others’ willingness to cooperate. This has important implications for communication in intercultural settings where members of diverse linguistic groups negotiate cooperative actions.