Human beings differ from all other living beings on earth. Although we are clearly like the animals, we also have the capacity to know and to communicate intelligently using language. This capacity to know is not just based on sensory perception and habit, but is an ability to know what and why a thing is. Without this capacity we would have no literature or philosophy.
Despite some headlines modern science has not shown that human beings are simply clever animals, if, by ‘clever’, we mean that all the intellectual abilities of human beings are found in other animals in less developed forms. Indeed, the very existence of science stands as a witness to the uniqueness of human beings, since other animals lack science at all. One could point to an almost infinite variety of other human activities, such as painting the Sistine Chapel or flying to the moon, to highlight the extraordinary uniqueness of human beings. The philosopher Wittgenstein expressed the difference as follows: a dog knows its master, but a dog cannot know that its master is coming home the day after tomorrow. In other words, other animals lack the ability to think of concepts like ‘the day after tomorrow’ or any abstract ideas, such as justice, truth and love. So non-human animals have no art, ethics, science, philosophy or anything involving such conceptual abilities. Furthermore, as G. K. Chesterton pointed out (Everlasting Man, I.1), a bird can display great ingenuity in building a nest, but once the nest is built the bird is satisfied. The bird does not go on to develop architecture, art or to discuss the meaning of life. All non-human animals are satisfied to be what they are. The human person, by contrast, seeks ultimate happiness and is discontent with any finite, created things alone.
Human beings also have a unique ability to choose, which gives rise to an enormous variety of human work and action, both good and evil. If our freedom is anything more than an emergent illusion it must exist somewhat independently of matter which is necessarily based on physical processes of cause and effect. Many philosophers have realised that the kind of being who knows and chooses in this way must have some quality which cannot simply be reduced to mere matter that is subject to change and decay. They therefore infer that we have immortal souls that do not perish when our bodies die.