Human beings are animals and have much in common with other animals, including at the mental level. Many animals have complex social interactions and emotional lives. Some species, especially chimpanzees, dolphins, and crows, have been found to have remarkable problem-solving abilities. And some animals use and even make rudimentary tools.
What, then, sets humans apart from other animals? According to Christian tradition, it is primarily that we have rational intellect and free will. Rationality involves, among other things, the capacity to understand abstract concepts and general statements, to make judgments of truth and falsehood, and to have insight into the laws of logic and mathematics as well as into the natures of things. Other animals, of course, know things and have a kind of understanding, but this is largely at the level of sensation and the “association” of one thing with another. While humans have this kind of knowledge too, we also have rational knowledge, which comes from making judgments of the truth or falsity of propositions. Other animals possess will and make choices, but they do not have “free will,” because their decisions do not involve reason and the choice of ends that can only be known through reason, such as justice or truth. Another term for free will is “rational will.”
Human reason is closely connected with language. While many other animals have complex communication systems, it seems that no other animals have language in the sense that humans do. Human language has hierarchical syntax, which allows the construction of an unlimited number of sentences of unlimited complexity.1 Human language also has abstract terms, or what philosophers call “universal terms,” which reach beyond what is sensed or imagined in “the here and now” to what can be grasped only by reason. Even chimpanzees, the closest extant relatives of Homo sapiens, when they are taught sign language, do not construct sentences but only combinations of at most two words. It is the power of abstract thought and language that has allowed humans to engage in the vast variety of activities, including science and mathematics, that have no counterpart among other earthly creatures.
Computers do many of the things that human minds do, such as receiving and processing data, storing information in memory, learning from experience, calculating, and making decisions based on complex weighing of factors. Computers can now play games such as chess more strongly than the best human players. None of this shows, however, that computers have abstract or conceptual understanding. In fact, very few people believe that computers (at least of the kind humans have so far built) even have consciousness, which would seem to be a precondition for abstract understanding or the other powers of reason. And certainly, no computer has free will.
Over the last century or more, various merely physical features or capacities have been pointed to as constituting what makes human beings distinctive, whether it be walking upright, making tools, or having opposable thumbs. The traditional Christian view, however, is that what fundamentally sets us apart is none of those things, but rather our possession of reason and free will, which still no animal or machine has been shown to possess.
1.. Why Only Us: Language and Evolution, Robert C. Berwick and Noam Chomsky (MIT Press, 2015).
Resources for further study
Why Only Us: Language and Evolution, Robert C. Berwick and Noam Chomsky (MIT Press, 2015). (“First Words” by Stephen M. Barr, First Things (April 2017) is an accessible summary and review of this book.)
Intellect: Mind Over Matter, Mortimer Adler (Macmillan, 1990).