Chimpanzees consider alternative possibilities.

Summary Humans reason not only about actual events (what is), but also about possible events (what could be). Many key operations of human cognition involve the representation of possibilities, including moral judgment, future planning, and causal understanding 1 . But little is known about the evolutionary roots of this kind of thought. Humans’ closest relatives, chimpanzees, possess several cognitive abilities that are closely related to reasoning about alternatives: they plan for the future 2 , evaluate other’s actions 3 , and reason causally 4 . However, in the first direct test of the ability to consider alternatives, Redshaw and Suddendorf 5 claim that chimpanzees are not able to represent alternative possibilities. Here, using a novel method, we challenge this conclusion: our results suggest that, like human cognition, chimpanzee thought is not limited to what is, but also involves reasoning about what could be the case.