Thought in the absence of language

As human beings, we spend a large part of our mental life imagining possibilities—situations that are not real. We often consider alternative possible worlds or reflect on how different versions of the past might have influenced the present. Reasoning about possibilities is essential for human survival, as it allows us to predict the future, plan our actions, and make better decisions. Despite its importance, the origins of reasoning about possibilities have been debated by philosophers and researchers for centuries. Currently, a major disagreement remains: is this kind of reasoning (and logical thinking more broadly) available to non-human animals and prelinguistic infants in the absence of language, or does it depend heavily on language and therefore only emerge in individuals capable of linguistic reasoning? The latter hypothesis is supported by recent experimental findings: when an object is dropped into an inverted Y-shaped tube and participants must catch the ball, animals and children under the age of 4 consistently fail to use both hands to cover the two exits of the tube (Leahy et al., 2022; Redshaw & Suddendorf, 2016). This has led to the proposal that animals and humans under 4 years of age are unable to represent alternative possibilities (Leahy & Carey, 2020). However, the Y-tube task is challenging because it requires children and animals to produce an optimal action regardless of which of the two outcomes occurs. We hypothesize that even younger infants and some animals might succeed at this task—that is, demonstrate an understanding that the ball could come out of either exit—if they were not required to produce such an action. This hypothesis is supported by recent data: chimpanzees succeed at a version of the Y-tube task when the required actions are more ecologically valid (such as pulling strings; Engelmann et al., 2021). As part of this research project, we will develop a task that implicitly measures whether children and infants—before the development of a fully-fledged linguistic system—are capable of representing multiple possibilities when no action is required from them.