Language as a mechanism for reasoning about possibilities

Many preschoolers do not distinguish the possible from the impossible in a marble-catching task

Do preschoolers differentiate events that might and might not happen from events that cannot happen? The current study modified Redshaw & Suddendorf's "Y-shaped tube task" to test how the ability to distinguish mere possibilities from impossibilities emerges over ontogenesis. In the Y-shaped tube task, the experimenter holds a ball above a tube shaped like an upside-down "Y" and asks a participant to catch it. A participant who identifies the two possible paths the ball can take should cover both exits at the bottom of the Y. But children might cover both exits without identifying both possibilities. For example, there are two good places to put hands, so they might just put one hand in each place. This does not require checking whether there is a path from the entrance to each exit. If children cover both exits because they have identified two possible paths for the ball, then they should differentiate exits where it is possible for the ball to come out from impossible exits, where there is no path from the entrance to the exit. In total, 24 36-month-olds and 24 48-month-olds were tested. Less than 20% of 36-month-olds and only about half of 48-month-olds distinguished between possible and impossible exits. Children who do not distinguish the possible from the impossible might not be evaluating possibilities at all. Results converge with existing literature suggesting that action planning that is sensitive to incompatible possibilities often emerges after the fourth birthday.

Thinking about possibilities: mechanisms, ontogeny, functions and phylogeny

Humans possess the remarkable capacity to imagine possible worlds and to demarcate possibilities and impossibilities in reasoning. We can think about what might happen in the future and consider what the present would look like had the past turned out differently. We reason about cause and effect, weigh up alternative courses of action and regret our mistakes. In this theme issue, leading experts from across the life sciences provide ground-breaking insights into the proximate questions of how thinking about possibilities works and develops, and the ultimate questions of its adaptive functions and evolutionary history. Together, the contributions delineate neurophysiological, cognitive and social mechanisms involved in mentally simulating possible states of reality; and point to conceptual changes in the understanding of singular and multiple possibilities during human development. The contributions also demonstrate how thinking about possibilities can augment learning, decision-making and judgement, and highlight aspects of the capacity that appear to be shared with non-human animals and aspects that may be uniquely human. Throughout the issue, it becomes clear that many developmental milestones achieved during childhood, and many of the most significant evolutionary and cultural triumphs of the human species, can only be understood with reference to increasingly complex reasoning about possibilities. This article is part of the theme issue 'Thinking about possibilities: mechanisms, ontogeny, functions and phylogeny'.