Four-year-olds incorporate speaker knowledge into pragmatic inferences.

Human communication relies on the ability to take into account the speaker's mental state to infer the intended meaning of an utterance in context. For example, a sentence such as 'Some of the animals are safe to pet' can be interpreted as giving rise to the inference 'Some and not all animals are safe to pet' when uttered by an expert. The same inference, known as a scalar implicature, does not arise when the sentence is spoken by someone with partial knowledge. Adults have been shown to derive scalar implicatures in accordance with the speaker's knowledge state, but in young children this ability is debated. Here, we revisit this question using a simple visual world paradigm. We find that both 4- and 5-year-olds successfully incorporate speaker knowledge into the derivation of scalar inferences. However, this ability does not generalize immediately to non-linguistic communicative contexts. These findings have important implications for the development of pragmatic abilities.