What is a Human, Really? Thinking about Definition via Aristotle

If your definition of a word is to be any good, Aristotle was the first to notice that it should say something general and something specific. Aristotle designated these two components the genus and species of a definition. Thus you might define human this way:

A human is an animal (genus) that is rational (species).

Or you could simply say:

Humans are rational animals.

Aristotle’s species component of a definition is sometimes referred to by the Latin word, differentia. And so, in definition, we have a general statement about a word accompanied by a differentia. Hence this too might be considered a definition of human (though perhaps not a good one):

A human is an animal that laughs. 

The reason a laughing animal is not quite as good a definition of the human as a rational animal is that one seems more essential to being human than the other. Or, at least, you could argue this (but don’t try it with someone who is British).

In any case, in seeking a good definition for a word, we want to identify, not just its unique properties, but its most essential qualities (and to foreground those). Aristotle’s own definition for the human was “political animal.” He believed that the most essential differentia about humans was their cultural behavior—their collective life in the polis (the city).   

But in defining something, we might also wish to say something a bit less obvious and concise, and be a tad more elaborate:

Humans belong to the small group of self-aware social mammals that includes chimps and dolphins. 

That’s a pretty clear answer to the genus question: humans are broadly or narrowly located within the hierarchy of living things, and most specifically within the kingdom of animals (or even more specifically, within the group of mammals that are self-aware and social). But notice that there’s no differentia on this definition yet.

Now for the differentia—the “species” designation. What distinguishes, in an essential manner, humans from other self-aware social mammals? In answer to this we might conclude the following: humans are uniquely characterized by their ability to reason, to speak, and to extend their influence and control over their environments via tools.

So this brings us to a pretty good definition for what it means to be human:

Humans are self-aware social mammals generally possessing the ability to reason, speak, and use complex tools.

But what if we preferred not to define ourselves, as humans, in relation to animals? There are, after all, other relations or hierarchies that we might wish to place humans in, and to do so would bring us to other definitions of what it means to be human. This is important to notice, for it reminds us that formal definition is always relational and set into some broader conceptual hierarchy of our choosing.

We might, for example, wish to define what it means to be human within the hierarchy of conceivably conscious beings (gods, angels, etc), in which case we might arrive at an answer to the genus question in which we share key characteristics, not with gods or angels (who are, presumably, immortal and free of materiality), but with aliens:

Humans belong to the group of conscious beings that are carbon-based, solar system dependent, limited in knowledge, prone to error, and mortal.

Unless they are quite far in advance of us, most conscious life forms beyond Earth are likely to share these characteristics with us. Hence the saying, “To err is human”, is also almost certainly true of many aliens (“To err is alien”). What makes us different is that we are on Earth, and so we might reach, after thinking about it some more, a genus-differentia definition something like this:

Humans are Earth-bound and body-limited conscious mammals.

In the conceptual hierarchy of conceivable conscious beings, the above definition distinguishes humans from gods (who are not Earth-bound or body-limited) and aliens (who are not of this Earth and have not evolved as mammals on our planet). And, in a pinch, we might make a genus-differentia definition that is really compact:

Humans are conscious mortals.


Humans are conscious earthlings.

But, really, this is inadequate because now we are being tapped on the shoulder by the chimps and dolphins (who are also quite self-aware and live on earth). So we might try again:

Humans are conscious and speech-producing mortals (or earthlings).

In relation to the gods and aliens, our mortality and Earth-boundedness comes to the fore of definition; in relation to other social animals, our rational, speech, and tool-using attributes come to the fore.

So all this chasing after what a human is really reminds us that definition is a way of arguing with yourself about what’s important. And notice that this definition of what a definition is also has a genus and a differentia! But, of course, it needs more thinking about and work (which tends to be true of everything we value).

About Santi Tafarella

I teach writing and literature at Antelope Valley College in California.

32 Responses to What is a Human, Really? Thinking about Definition via Aristotle

  1. Humans are the only self aware animals that worry about their place in the universe and are dissatisfied with simply living.

    At least I think so 🙂 But humans seem dissatisfied even in good times, wondering of the beyond. It does not seem that other self aware critters do this.

    • liggamite says:

      yes jared, that is who we are. we can never be content, it built into us. Think about this for a second…say hitler took over the planet. Then what? he has it, he’s won, who cares? he’d still not be happy. We struggle to complete things, just to prolong the existence of our species. Life really has no purpose, no sole mission. So just enjoy it

    • auz_ says:

      Humans go after what they think will make them happy. But when they get it, it does not. They do this over and over again and expect a different result. If the definition of insanity is doing the same thing over and over again and expecting a different result, then is not the entire human race insane.

  2. Paradigm says:

    We may have originated on some other planet and exist in various forms throughout the universe. And what we call aliens may in fact be an earthbound social mammal. After all, UFOs are spotted on radar near the planets surface but rarely in space. Before they were called aliens the same stories were told of fairies.

  3. TomH says:

    The Creator defines the creation. Humans are those creatures made in the image of God.

    • santitafarella says:


      Your definition also has a genus and differentia (and is another way of looking at it).


    • The one says:

      The idea of that disgusts me if anyone was to create an image of himself what was that purpose and if he created humans as an image of himself why towards the end of a humans life must there be death

      • Pedro says:

        there has to be an end to everything

      • auz_ says:

        according to theology, the first two humans were made in the image of God and were then deceived by Satan ( God’s previous right-hand-man, he tried to overthrow him ) into deliberately disobeying God’s orders to not eat of the tree in the center of the Garden of Eden. this being the first act of “sin” brought death and evil into the world.

  4. liggamite says:

    soon, humans will be immortal. it’s the truth. just wait
    P.S. i’m not psycho 😉

  5. Where would we be without differentia? How about that capacity as what defines us…Our category is that we categorize. In this sense we haven’t really got beyond Aristotle.

  6. Peter Smith says:

    The article and the comments are astonishing, not for what they say, but for what they don’t say.
    Here is Santi’s approved definition:

    Now that seems a pretty good definition, so what is wrong with it?

    Think about the history of our species. It is the story of great wrongs, wars, massacres and the efforts of groups to dominate or enslave other groups, interleaved with the heroic efforts of some groups to advance ethical behaviour. All of these acts are essentially moral in nature. In fact almost every decision we make has a moral component.

    The sociologist, Christian Smith, in his book, Moral, Believing Animals concludes

    This book has advanced one approach to answering this question, arguing that the most adequate approach to theorizing human culture and social life must be a normative one that of humans as moral, believing, narrating animals and human social life as constituted by moral orders that define and direct social action. Human culture, I have suggested, is always moral order, and human cultures are everywhere moral orders. Human persons, I have claimed, are nearly inescapably moral agents, human actions necessarily morally constituted and propelled practices, and human institutions inevitably morally infused configurations of rules and resources.


    So, moral order is a defining part of our human species. This could be reflected by updating Santi’s definition as follows:

    Humans are self-aware social mammals generally possessing the ability to reason, speak, and use complex tools, acting in a society ordered by a set of implicit or explicit moral norms.

    What I find so revealing is that no one thought to mention the moral component.

  7. Anonymous says:

    humans might be seen as a red herring. Language might be the organism we are talking about

  8. femina says:

    I like your website stumbling across it when looking at definitions of ‘human’. It leaves me wondering about a few things, such as transmission of thought. But if you are curious about the why, look into my website Sozieterna

  9. Pingback: Research Sources | What It Means To Be Human

  10. Haider says:

    Humans does not animals

  11. Tharaka Mohotti says:

    We are humans….we know what we are.we have visions and missions to do.humans are the greatest source in the world.they are not the creators of the world…they are the wonders of the world who make the world a world.they are un valued un measured.humams are the universe or the background of the world

  12. Ankit says:

    Man is the master piece of god that can judge right or wrong

  13. Neale says:

    A human being is a self aware animal who embraces values, ethics, morals and principles higher than that of a the self preseving (selfish), instinct driven only, animal self.
    By this definition many, if not the majority, of the genus Homo and species sapiens do not qualify as being “human”.

    • Santi Tafarella says:

      I would make the distinction (which you’re not doing) of distinguishing behavior from capacity. In other words, if you have the capacity to laugh, but rarely or never do, you nevertheless belong to those creatures with that capacity.

      • Neale says:

        Laughter is cruel, humour ALWAYS has a victim, even if it’s self. There is nothing higher in laughter, only the cruel take delight from other’s pain and suffering. Humanity and being human is an IDEA, not a species.

  14. Anonymous says:

    Humanity’s greatest achievement will only and ever be the destruction of life and the birth of life.

  15. Steve Waclo says:

    So, how do people in the grips of severe dementia fit in? Do they remain human?

  16. Very interesting question… do you have an answer??

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