In 1984, the philosopher Aaron Sloman invited scholars to describe ‘the space of possible minds’. Sloman’s phrase alludes to the fact that human minds, in all their variety, are not the only sorts of minds. There are, for example, the minds of other animals, such as chimpanzees, crows and octopuses. But the space of possibilities must also include the minds of life-forms that have evolved elsewhere in the Universe, minds that could be very different from any product of terrestrial biology. The map of possibilities includes such theoretical creatures even if we are alone in the Cosmos, just as it also includes life-forms that could have evolved on Earth under different conditions.

We must also consider the possibility of artificial intelligence (AI). Let’s say that intelligence ‘measures an agent’s general ability to achieve goals in a wide range of environments’, following the definition adopted by the computer scientists Shane Legg and Marcus Hutter. By this definition, no artefact exists today that has anything approaching human-level intelligence. While there are computer programs that can out-perform humans in highly demanding yet specialised intellectual domains, such as playing the game of Go, no computer or robot today can match the generality of human intelligence.