8. Can We Really Know if the People Around Us Are Conscious?

A short meditation on Descartes, simulations, and the old dream of certainty

We’ve all heard the question, usually framed in slightly dramatic tones:“But how do you really know anyone else is conscious?”The suggestion is that perhaps everyone else is just an automaton. That maybe you’re the only one with inner experience, and everything else, the chatter, the smiles, the whole of society, might just be a simulation.

It’s a strange and alluring thought. But where does it come from?

1. Descartes’ Demon

This scepticism about other minds has a long history, and one of its clearest expressions came from René Descartes in the 17th century. Sitting alone in a room, Descartes tried to strip away every belief that could be doubted. What if everything I think I know, the world, my body, even mathematics, is an illusion, a dream, a trick played by some malevolent demon? A devilish force that manipulates my perceptions and beliefs, deceiving me at every turn?

In the face of this total doubt, Descartes landed on one unshakable truth:“Cogito, ergo sum”: I think, therefore I am. Even if all else is false, the very act of doubting confirms that someone is doing the doubting. Thought is self-validating.

But what about other people? Descartes’ methodical doubt meant he could no longer take for granted that others were like him. Even they might be illusions.

This marked the beginning of what philosophers call the “problem of other minds.” If consciousness is internal, subjective, and invisible, how can I ever really know that someone else has it?

2. The Modern Simulacrum

Centuries later, the same worry plays out in different forms. But the devil has changed shape. Today’s sceptic doesn’t fear a demon, they fear the algorithm, the matrix, the chatbot that passes for a human. The synthetic being that mimics personhood.

We live in an age of simulations, where digital avatars, deepfakes, and AIs perform fluency, empathy, creativity. The uncanny resemblance to human traits brings back the old Cartesian doubt in a shiny new package. We might ask: “How can I know this is real consciousness, and not just a simulation?”

In one sense, this doubt is philosophical play, and a valid epistemological quest. But it’s also culturally revealing. We’re haunted by illusions, not because we truly believe we live in a dream, but because we’re saturated with interfaces, performances, and proxies for life. The simulation question emerges because simulation is now the water we swim in.

3. So… Can We Know if Others Are Conscious?

Let’s return to the original question. Are the people in the room with you at any given moment, your colleagues, your partner, the person across from you on the train, really conscious? The philosophical answer is cautious: you can never know with 100% certainty. You can’t look inside their heads. All you see is behaviour. For all you know, they might be zombies or holograms.

But the practical answer is different. You can know, to a high degree of probability, that others are conscious, just like you. Why? Because there are observable, testable attributes that correlate with what is commonly thought of as linked to consciousness:

• Sentience: They react to pain and pleasure in intelligible ways.

• Self-awareness: They can refer to themselves, reflect on their identity, and show continuity of thought.

• Responsiveness: They engage with the environment, hold conversations, adapt to new information.

• Biological life: They grow, metabolise, sleep, and bleed.

• Experience: They will be able to relate their experiences to you and others.

You trust that the person next to you is conscious not because you have direct access to their mind, but because of shared language, shared embodiment, shared vulnerability. These signs of life and inner experience are not illusions, they’re the basis of society, trust, empathy, and ethics. We don’t demand 100% certainty in any other area of life, we act on evidence, inference, and experience. The same holds true here.

4. Why Do We Keep Asking?

Still, the question lingers, and that’s the most interesting part. Why are we so drawn to doubting the things around us, or within us, are true or valid? Why do we love to entertain the idea that everyone else might be a robot, that our very life might be an illusion, a trick?

Partly, the answer may simply be a natural product of the enquiring mind. Descartes's questioning isn't limited to his own epoch. It’s a philosophical impulse. And partly, it’s existential. It speaks to our fear of isolation. Our inability to fully access another’s experience. Our sense that the mind is always, in some way, alone.

This doubting is nothing new. Aristotle wondered whether spiders had minds. Thomas Nagel famously asked what it was like to be a bat. Indian philosophy asked whether consciousness could reside in a stone, or pervade all things. These are ancient questions.

5. A Zeno’s Paradox of Knowledge

Zeno, the Greek philosopher, proposed that motion is an illusion. If you want to get from A to B, you must first get halfway. But before that, halfway to halfway. And so on. An infinite series of smaller and smaller steps means, in theory, motion could never begin. Zeno told the story of Achilles who could never catch up with the tortoise in a race, who had got a headstart.

Aristotle, Physics VI:9, 239b15

And yet, we move. We live. We get there. So too with knowledge. You can divide certainty into ever smaller doubts. You can attempt to quantify degrees of certainty with ever increasing values. But in the end, we still act, still believe, still connect. We may never reach absolute certainty about the consciousness of another. But that’s not a flaw in our reasoning, it’s a feature of being human, and of being in a world filled with others we cannot fully know.