When children hear a novel term in the context of two potential referents--one familiar or already-named, and one novel--they tend to assume that the novel word picks out the unfamiliar referent, a pattern typically described as the “Mutual Exclusivity” (ME) effect. In a typical demonstration of ME (Markman and Wachtel 1988 et seq.), children are presented with two objects -- one of them is novel and the other has a familiar label (e.g. a car). Next, they are asked, e.g. to “Show me the dax!”; children as young as 17 months of age (Halberda 2003) reliably choose the as-yet unlabeled object. While there are several competing explanations for why children (and adults) in these tasks treat dax and car as being mutually exclusive in reference, all of them invoke a bias to avoid applying two labels to the same object. This study explores an alternative hypothesis that the exclusivity inference, and in turn the choice of referent, depends on the information structure of the carrier sentences. Information structure is a cover term for a set of pre-theoretic concepts (focus, givenness, topicality) that have to do with discourse coherence. We take a fairly standard (in Linguistics) assumption that information structure is an aspect of the syntactic representation of sentences, with specific rules for intonation and semantic interpretation. Relevantly here, we assume the existence of two distinct markers that serve to relate a sentence, and the information expressed by it, to the surrounding discourse (Kratzer & Selkirk, Buring, Schwarzschild): Givenness (G) markers, which are sensitive to whether the meaning of an expression has been made salient in and thus recoverable from the preceding discourse; given expressions are de-accented/de-stressed. Focus (F) markers, which evoke alternatives to an expression, thereby establishing contrast with some part of the preceding discourse; focused expressions are emphasized/stressed. Together, G- and F- markers signal which parts of a given sentence matches (is anaphoric to) and contrasts with parts of the surrounding discourse. Here, we test the hypothesis that mutual exclusivity inferences can arise in a ME-paradigm as a result of the selective use conditions (emphasis/stress or lack thereof) imposed by G- and F- marking. While past studies did not systematically manipulate this variable to our knowledge, we suggest they may have tended to present their linguistic stimuli as in (3), with prosodic prominence--and thus, presumed F-marking--on the novel label. We think this is likely because that is the grammatical way, in standard English, to refer to an object that is being introduced into the discourse for the first time. Look at the car. Now look at [the DAX]F. The use condition on F-marking demands that the context makes salient a distinct alternative to dax (i.e. a contrasting meaning). There is only one salient alternative to dax, namely car. In order to meet the use conditions on F-marking, car must not entail dax, i.e. dax must not be another name for car, nor should dax be a subtype of car. Therefore, the dax must not pick out something that can be picked out by the term the car, i.e. the item already pointed to. If contrast between F-marking and G-marking, rather than contrast between the labels, drives ME-effects, we predict that removing the F-marker should result in a change in referent selection even as the labels stay the same. If, instead, dax was G-marked (indicated by prosodic de-accenting), the comprehender should look for something in the preceding discourse that has already made salient the relevant meaning. In this case, ME-effects should no longer arise -- G-marking should lead participants to infer that the previously labeled and known object -- the car -- can be referred to as a dax. In this study, we manipulate F- and G- marking on the prompted noun-phrase and ask whether rates of ME-driven selection shifts as a consequence. In the first version of our paradigm, we seek to establish whether the cues in information structure alone are sufficient to produce an ME effect when the nouns/labels do not necessarily contrast. To avoid a contrast between a known and a novel label, we will show participants two novel objects. First, we will unambiguously label one of two objects (e.g. blicket). Then in our test phrase we will use the NP “the toy” either F-marked, or G-marked with corresponding predictions of how children should interpret them. We use the noun-phrase “the toy” instead of “the dax” as the target phrase that probes the ME effect because “toy” could be -- but does not have to be -- a superordinate category that describes both objects. The use of non-contrasting labels might make ME-inferences (the blicket is not a toy) less likely while making co-referential readings (the blicket is a kind of toy) more likely as a whole. This creates the condition to test whether information structure alone can induce an ME effect, independently of whether contrast between labels is also sufficient to do so. When hearing F-marking on “the toy”, children should assume that “the toy” is an alternative to a salient discourse antecedent - in particular one that cannot entail toy. The only salient antecedent is “blicket”. What follows is that “blicket” cannot entail toy. If this is true then it follows that the referent of “the toy” can only be the other object. On the other hand, when “the toy” is G-marked children should assume that the meaning is recoverable from the available discourse. As “blicket” is the only salient discourse antecedent they should assume that “the toy” refers to that.