Do we know we are not, right at this moment, dreaming? That we even exist?

Level 1: Beginner

Vocabulary

• Senses (noun): The ability to see, hear, touch, smell, taste, and feel.

• Trick (verb): To make someone believe something that is not true.

• Shadow (noun): The dark shape caused by something blocking light.

• Doubt (verb): To think that something is maybe not true.

• Certain (adjective): To be sure about something / to be 100% about something.

• Prisoner (noun): A person who is not free and cannot leave.

• Exist (verb): To be real.

Text

In the film The Matrix, Morpheus asks Neo, how does he know what is really real? 

The world of the Matrix feels real. In it, objects are hard and pain hurts. Computers created this world, but the people inside it do not know this.

So, how do we know our senses are not being tricked?

Two thousand years ago, the Greek philosopher Plato told us to imagine some prisoners in a cave. They cannot move. They can only look at a wall. There is a fire behind them and people walk in front of the fire with different objects. 

The prisoners can only see the shadows of these objects on the wall. They cannot see the objects directly, and so they think the shadows are the real objects.

What happens if one prisoner becomes free and turns around?

The prisoner will learn that the shadows are only a small part of a bigger world.

Plato thought that maybe our senses only show us part of the world. But he thought if we learn and improve our minds we can understand the truth. 

But there is another problem. After the prisoner becomes free or Neo leaves the Matrix, how can they know that this new world is really real?

They still use the same mind and senses to understand this new world.

What if we cannot always trust our senses or our minds?

René Descartes thought the same thing. He was born in France in 1596. He lived at a time of big changes in science.

Descartes wanted to find something he knew 100%. Something that was completely certain.

Think about building a house. You need strong ground under the house. If the ground is weak, the house might fall. He thought the same thing about what we know. 

First, he looked at the senses.

We learn many things through seeing, hearing, and touching. But our senses sometimes make mistakes. For example, a straight stick can look bent in water.

But maybe we can still be sure about simple things. I can see that I am sitting in a room, for example.

But just like in the Matrix, dreams can trick us about even simple things. 

Dreams can feel real while we are dreaming. In dreams, we talk to people and we see places. But we do not know we are dreaming.

So how can we know that we are awake now? Maybe this is all a dream.

But what about maths? Two plus three is five, even in a dream.

Descartes wanted to doubt this, too. He said imagine an evil god. This evil god can control your mind. It can make you wrong about even maths every time.

Descartes did not really believe in an evil god. But now he had a reason to doubt everything. He doubted his senses. He doubted the world. He doubted his own mind.

But then he found something he could not doubt.

He was thinking.

Maybe an evil god can trick him about the world. But Descartes was still thinking about it.

If he thought, “I am not thinking”, he was still thinking.

And if he was thinking, Descartes thought that he must exist.

This gives us his famous words:

Cogito, ergo sum – I think, therefore I am.

Descartes found one thing that was certain.

There was still a problem. The evil god could still trick him about everything else. 

Descartes used the idea of a perfect God to help him.

A perfect God would not trick us in this way. So, if a perfect God exists, we have a reason to trust our minds again.

So why believe in a perfect God?

Descartes said he was not perfect, but he had the idea of a perfect God in his mind. He said that someone who is not perfect cannot make this idea alone. So, he thought that the idea must come from something perfect. From God. 

Many philosophers see a problem here. They think his idea goes in a circle. He believes in God because of his mind. And he trusts his mind because of God.

Because of this, many people think Descartes did not reach his main goal.

However, his ideas were still very important for philosophy.

He asked us, “How do we know what is real?”

We see and hear information every day. Sometimes it is true, and sometimes it is not. That means Descartes’ question is very important for us today. 

Your turn

Here are some questions to increase your understanding and help you remember any new vocabulary. Try answering them with a friend or tutor, or write the answers down. Try to use any new vocabulary in your answers.

• Can you always trust what you see and hear? Why or why not?
  
• How do you know that you are awake now?
  
• Think of something you believe. How do you know that is true?

Did you find this level of English comfortable? Then congratulations! Now you can try the next level of difficulty below.

Level 2: Intermediate

Vocabulary

• Reliable (adjective): Can be trusted to work correctly or tell the truth. 

• Method (noun): An organised way of doing something. 

• Certainty (noun): The state of being completely sure about something, with no doubt at all. The adjective is certain.

• Illusion (noun): Something that looks or feels real but is not.

• Doubt (verb/noun): To be unsure that something is true. 

• Reason (noun): Our ability to think carefully and work things out. / the cause or explanation of something.

• Trick (verb): To make someone believe something that is not true.

• Fault (noun): A mistake or weakness / something wrong with a person or thing.

• Senses (noun, plural): The natural abilities we use to experience the world: sight, hearing, touch, taste, and smell.

Text

Have you ever had a dream, Neo, that you were so sure was real? What if you were unable to wake from that dream? How would you know the difference between the dream world and the real world?

Morpheus, The Matrix (1999).

In The Matrix, Morpheus presents Neo with a simple problem. If an experience felt real enough, and if there were no way to leave it, how could we tell the difference between illusion and reality? 

After all, the world of The Matrix appears to be real in every important way. Objects are solid and pain feels painful. All of this is created by computers. But to those in the Matrix, the experiences feel completely real.

This creates a problem about knowledge. Normally, we trust our senses to tell us what is real. But what if a fake world felt exactly like the real world, so that you could not tell the difference? How could our senses tell us anything certain about the world outside our minds?

Two thousand years ago, the Greek philosopher Plato asked us to imagine prisoners trapped in a cave, tied up and forced to stare at a wall for their entire lives. Behind them burns a fire; between the fire and the prisoners, people carry objects whose shadows appear on the wall. The prisoners spend their whole lives seeing only the shadows, never the objects themselves.

These shadows are all they have ever experienced, and so they believe them to be reality. But what if one of these prisoners were set free and able to turn around?

The prisoner would slowly realise that what they had experienced before was just a small part of a much wider and more complex reality.

Plato did not think that knowledge was impossible. Instead, he thought our senses might show us only part of reality. Better thinking can help us understand more through education and reason. 

After leaving the cave or escaping the Matrix, how could we know that we had really done so? Can we be certain it is not just another illusion? We are still using our minds and senses to decide if this new world is real or not. 

What if our senses and our reason cannot always be trusted?

Enter René Descartes, born in France in 1596. He lived during a time of big changes in science and ideas, often called the Scientific Revolution. It was during this period of time, when many basic beliefs were being shown to be wrong, that Descartes began his search for certainty.

His thinking went like this: How can we be certain of our beliefs if the main source of those beliefs is itself uncertain?

For example, Descartes said if you build a house, you cannot build it on loose soil. The ground might move, and the unstable house will fall down after a time. Instead, you dig and dig until you reach hard rock. This is something solid and strong to build on. 

Descartes looked at where those beliefs came from: the senses and reason. If he had reason to doubt these, then he would throw them away and say they are not certain enough. 

Descartes is not looking for a way of thinking that we could actually use in normal daily life. Instead, he is looking for a completely certain base on which it would be safe to rebuild science and our knowledge.

He started with the senses.

Many of our beliefs about the world come from our senses. We see objects, hear sounds, touch things, and then decide from these experiences that there is a real world outside our minds.

But our senses are not always reliable. A straight stick may look bent when underwater; we may hear certain words or sounds incorrectly. For Descartes, the senses are too easily tricked to trust fully.

But we can usually trust our senses for most things, right? I am certain that I am sitting down right now after all. But Descartes found reason to doubt even this. 

What if this is just a dream?

Dreams are a problem for philosophy because they can feel like normal experiences. We may dream of walking down a street or speaking with a friend, but neither of these experiences is real. The problem is that most of the time, while we are inside the dream, we do not realise that we are dreaming.

So what can make us sure that we are not dreaming right now? How can we be certain that things which seem obvious to our senses, such as the fact that I am sitting on a chair, are not illusions inside a dream?

But some things must be certain. Like maths, a triangle always has three sides, even in dreams. Two plus three always equals five. 

Descartes can doubt even this. He imagines a powerful evil god that can control not only what we see and hear but also the way we think and reason. We could be wrong every time we think two plus three equals five because the evil god is affecting our minds.

Descartes did not believe an evil god really existed. But even the possibility was enough to let him doubt our reason.

Without our reason and without our senses, we seem to be left with nothing certain. What about our own existence, the fact that we are alive and here at all? Could the evil god be so powerful that we are even wrong about this?

Now, finally, Descartes finds something he cannot doubt.

The evil god could trick Descartes about everything he was thinking about, but not about the fact that he was actually thinking. If Descartes doubted that he was thinking, that doubt would itself be a thought. So, by saying that thought did not exist, he would actually show that it did.

This is why it is different from his earlier doubts. Doubting the existence of the outside world does not make the outside world exist. Doubting whether we are awake does not show that we are awake. But doubting that we are thinking is different, because the doubt itself is a thought.

And if thought exists, Descartes believed there must be something doing the thinking.

This leads us to Descartes’ most famous statement:

Cogito, ergo sum – I think, therefore I am.

So, what now? He has his one certainty. He knows that he exists, but what can he do with it? Well, there was still the problem of the evil god, who could even trick him about the most basic things.

To solve this problem, Descartes uses the idea of a perfect God. A perfect God would not trick us, because tricking people is a fault, and a perfect being cannot have faults. This does not mean that we can never be tricked. But Descartes believed it meant that our minds were not always wrong from the start, like they could have been if an evil god created them. So, we have a reason to trust our ability to think again.

So why did he think we should believe in a perfect God?

A very simple version of one of his arguments goes like this: He may be wrong about everything, but he still has the idea of a perfect God in his own mind. Where could such an idea have come from? He thought that an imperfect mind could not create the idea of a perfect thing by itself, so some other perfect thing must have put the idea there. God. 

There are many problems with this idea and the way he uses it. For example, his thinking may go in a circle. He can trust reason because of a perfect God; he believes in a perfect God because of reason. Descartes is using reason to show that God exists, but God is meant to show that reason can be trusted.

For many people, this is where they give up on Descartes. Many would say that his main goal failed because he did not rebuild all beliefs on something certain, even if he did find something certain. 

But his work was still very important. His method of doubt is often described as the beginning of modern philosophy. Instead of first asking what exists, philosophy started to ask more and more: What can we know? And how can we know it?

And while his exact method of doubt is not practical for normal life, the need to doubt and question how we know things is very important in a world where a great many “gods” are trying to convince us, or trick us, every single day.

Your turn

Here are some questions to increase your understanding and help you remember any new vocabulary. Try answering them with a friend or tutor, or write the answers down. Try to use any new vocabulary in your answers.

• If your senses can sometimes trick you, how much should you trust what you see and hear?
  
• Do you think Descartes was right that thinking proves you exist? Why or why not?
  
• Is it useful to doubt your own beliefs sometimes, or can too much doubt become a problem?
  

Did you find this level of English comfortable? Then congratulations! Now you can try the next level of difficulty below.

Level 3: Advanced

Vocabulary

• Faculties (noun, plural): The natural powers of the mind and body, such as sight, memory, and the ability to reason.

• Perception (noun): The way we take in and understand the world through our senses. The verb is to perceive.

• Indistinguishable (adjective): So similar to something else that you cannot tell the two apart. 

• Self-evident (adjective): Obviously true / needs no proof or explanation.

• Self-undermining (adjective): Describing an action or statement that destroys itself in the act of being made.

• Sceptical (adjective): Doubtful about something / not easily convinced that something is true.

• To set [something] aside (phrasal verb): To put something to one side and stop considering it, usually temporarily. 

• Beyond a shadow of a doubt (idiom): Completely certain, with no possibility of being wrong.

• A sliver of doubt (phrase): A very small amount of doubt. A sliver is a thin, narrow piece of something.

• To be but a [something]: An old-fashioned way of saying ‘to be only a…’. 

• Runs thus: A formal way of saying ‘goes like this’, used to introduce an argument or explanation.

Text

Have you ever had a dream, Neo, that you were so sure was real? What if you were unable to wake from that dream? How would you know the difference between the dream world and the real world?

Morpheus, The Matrix (1999).

In The Matrix, Morpheus confronts Neo with a deceptively simple problem. If an experience were sufficiently convincing, and if there were no possibility of leaving it, how might one distinguish illusion from reality? The film, of course, provides Neo with a way out of this illusion. But Morpheus’ question is more radical than the story that follows it, and indeed, it is the question, as much as the story, that should trouble us.

After all, the world of The Matrix appears to be real in every meaningful sense. Objects are solid, pain feels painful, and causal relations operate normally. All of this generated by computers. Yet to those in the Matrix, the experiences are as real as ever.

The problem that then arises is epistemological, a question of knowing and knowledge. On the ordinary common-sense view, perception provides us with knowledge about reality. But if a simulated reality were subjectively indistinguishable from a “real” one, so that you could not tell the difference, and if it were all we had ever known, then how could our ordinary perceptions tell us anything certain about the external world?

Such questions are not new. The Greek philosopher Plato, over two millennia earlier, asked us to imagine prisoners confined to a cave, chained tightly, and forced to stare at a wall for the entirety of their lives. Behind them burns a fire; between the fire and the prisoners, people carry objects whose shadows are projected onto the wall. The prisoners spend their whole lives only ever seeing the shadows, never the objects themselves.

These shadows constitute the entirety of their experience, and so naturally they take them to be reality. Yet, what if one of these prisoners were to be released, to be freed of their chains and to turn around? How might they understand this new world before them?

At first, it may appear to them that the objects themselves are less real than the shadows they had experienced their whole lives. Only gradually would the prisoner realise that what they had experienced before was just a small part of a much wider and more complex reality. Now imagine how it would seem if they tried to convince their fellow prisoners, still chained in a world of dancing shadows, of this fact. To say they would find it difficult would be an understatement.

Plato was not totally sceptical about our ability to know, however. Rather, he was suggesting that ordinary sense experience may give us only a limited and distorted understanding of reality and that an improvement in our reasoning can help overcome this. Indeed, both Plato and The Matrix arrive at quite optimistic conclusions. Through education and reason, the prisoner gradually moves beyond appearances towards a deeper form of knowledge, eventually reaching the world outside; Neo leaves the Matrix and discovers that what he took to be reality was not just an incomplete picture, as the prisoner’s shadows were, but a complete fabrication.

Yet both Plato’s optimism and Neo’s acceptance of the world outside the simulation present us with a further problem.

After leaving the cave or escaping the Matrix, how could one know they have genuinely done so? Can one be certain that this new world is not just a further illusion? After all, the very same faculties are being used to assess both situations. When Neo chooses the red pill, it is the reasoning and senses grown and shaped by the simulation of the Matrix that do so. When the prisoner learns about the cause of the shadows dancing on the wall, it is with the same mind that led them to believe those shadows were a complete picture of reality in the first place.

What if it is those faculties, our senses, our reason, that are unreliable?

Enter René Descartes, born in 1596, France.

Descartes was a polymath: someone whose expertise spans multiple subjects and fields. He lived through a period of intellectual transformation: the so-called Scientific Revolution, in which he was an active participant, writing several works. It was in this period, when so many fundamental assumptions were being challenged or proved false, that Descartes set out on his mission for certainty.

His reasoning ran thus: How can we be certain of our beliefs if the foundational source of those beliefs is itself uncertain?

To paraphrase a metaphor from Descartes himself: if you build a house, you cannot just build it on top of the soil; it is always shifting, and the unstable house will eventually collapse. Instead, you dig and dig, ignoring any loose soil until you reach hard bedrock, unshakeable and strong.

Rather than examining every single belief, an impossible task, Descartes examined the sources those beliefs came from, namely the senses and reason. Any source he had the slightest reason to doubt would be set aside, along with all the beliefs that derived from it. His goal was not to search for beliefs that were merely reasonable, probable, or supported by strong evidence. He wanted to discover whether anything could be known with complete, unshakeable certainty. 

For clarity’s sake, we should recognise that Descartes is not looking for a philosophy by which one could actually live their life. Instead, he is looking for a truly certain foundation upon which it would be safe to rebuild science and our systems of knowledge.

So, where does he start in his method of doubt? With the senses.

Many of our beliefs about the world arise through perception. We see objects, hear sounds, feel surfaces, and then infer from these experiences that a corresponding external world exists. 

Yet sensory perception is not infallible, not perfectly reliable. I am sure we have all experienced illusions. A straight stick may appear bent when underwater; we mishear certain words or sounds. We even exploit our own senses’ tendency to be misled when we create movies, games, and art, making two-dimensional worlds appear three-dimensional.

For Descartes, this was enough to undermine the senses as a source of absolute certainty. They are simply too easily tricked.

The fact that our perceptions are sometimes wrong is perhaps not enough to doubt everything they inform us about. After all, a person may reasonably acknowledge occasional perceptual errors, like those mentioned above, while remaining certain that they are sitting in a room, in a human body, surrounded by physical objects.

Descartes therefore requires a more powerful argument. And so he turns to the world of dreams.

Dreams are philosophically troublesome because they can feel like ordinary experiences. One may dream of walking down a familiar street or speaking with a friend without recognising, at the time, that neither of these experiences is real.

The problem is not that waking life and dreaming are always indistinguishable. We recognise the flaws in our dreams the moment we awake, after all. The problem is that most of the time, from within the dream itself, the dreamer does not recognise they are dreaming.

There seems to be nothing to guarantee that we are not, right at this moment, dreaming. That the things so obvious to our senses, things beyond a shadow of a doubt, such as that I am sitting on a chair or writing with my hands, are not illusions within that dream.

You may be thinking, some things remain certain whether they are in a dream or not. A dreamed triangle may not exist as a physical object, but it still possesses three sides; two plus three is still five; a statement cannot be both true and false at the same time.

Perhaps the senses are vulnerable, while mathematics or certain axioms remain secure.

Descartes doubts even this. He imagines a powerful deceiver, an evil god, capable of manipulating not only our sensory experiences but our cognitive faculties themselves. In reality, we could be mistaken every time we think two plus three equals five because of the evil god’s meddling in our very minds.

While he did not believe such an evil god actually existed, the mere possibility was enough to introduce a sliver of doubt about our reason.

So now we have at least some cause to doubt our senses; they are often inaccurate and could be doubted entirely, since this could be but a dream. We also have cause to doubt our own logic and reason, as a sufficiently powerful being could alter our very minds.

Again, it is worth emphasising here: Descartes does not mean for this to be a method to live one’s life, nor does he claim that our senses, reason, logic, and all knowledge that comes from them are not justified. He is merely looking for something that is truly certain and beyond any doubt.

Yet we have exhausted everything; without our reason, without our senses, we appear to be left with nothing certain. What about our own existence? Could the evil god be so powerful that it deceives us into falsely believing that we exist?

Now, finally, Descartes encounters a limit to his doubt.

The evil god could deceive Descartes about everything his thoughts represent, but not about the fact that thought is occurring, since the occurrence of thoughts is immediate and self-evident. If Descartes doubted that he was thinking, that doubt would itself be an act of thought and so, by denying the existence of thought, he would actually confirm it.

This is why it differs fundamentally from his earlier doubts. Doubting the existence of the external world does not make the external world exist. Doubting whether one is awake does not prove that one is awake. But doubting whether one is presently thinking is self-undermining, because the doubt is itself an instance of thought.

And if thought exists, Descartes believed there must be something doing the thinking.

This leads us to Descartes’ most famous formulation:

Cogito, ergo sum – I think, therefore I am.

The Cogito is frequently interpreted as though it were a syllogism, as seen below:

P1: Everything that thinks exists.

P2: I think.

C: Therefore, I exist.

However, viewing it as a simple syllogism introduces a problem. If our reason and logic are not certain, then nor are their results, syllogisms included.

Instead, perhaps, as some philosophers have done, we should view the statement as self-verifying or performative. In thinking, ‘I do not exist’, I am performing an act that cannot occur unless I exist, since, as Descartes believed, thought requires a thinker. For him, this was certain proof of his own existence.

So, what now? He has his one certainty, but what can he do with it? Can he use this to find anything else that is certain? He considered what made the existence of thought so sure when he could doubt even the chair he was sitting on.

His answer was that he perceived it ‘clearly and distinctly’. Clearly because it could not be overlooked or hidden; distinctly because it was not mixed up with anything in doubt. He decided then that whatever else he could perceive as clearly and distinctly as he perceived his own thoughts must also be true. He used the Cogito as a standard to measure other beliefs against. But there was still the problem of the evil god who could even deceive him about the most basic of things, and seemed to limit him to that single point of certainty: that he exists as a thinking thing.

To overcome the problem of the evil god, he turns to the idea of a perfect God. A perfect God would not deceive us, since deception is a flaw and a perfect being has no flaws by its very definition. While a perfect God does not guarantee that we are never deceived – after all, people lie to each other all the time – it guarantees that our minds themselves are not built in a way to be deceived from the very start by some evil god. So, we have cause to trust our reason again.

So why believe in a perfect God? An extremely simplified version of one of his arguments for the existence of a perfect God runs thus: He may be deceived about everything, but he still finds the idea of a perfect being in his own mind. Where could such an idea have come from? He thought a finite and imperfect mind cannot invent perfection out of nothing, so something perfect must have placed it there.

Many objections to his arguments for a perfect God and how the idea is used have been proposed. For example, the logic is possibly circular, although this is contested. He can trust reason because of a perfect God; he believes in a perfect God because of reason. Descartes is using the reliability of reason to establish the existence of the very God who is supposed to guarantee that reason is reliable. 

For most, this is where their journey with Descartes ends, and many would claim his main project was a failure, that he did not rebuild human knowledge on certain foundations. But his work was certainly not in vain. His method of doubt is often described as the birth of modern philosophy. Instead of first asking what exists, philosophy increasingly took as a starting point what we can know, and how we can know it, and philosophers spent the next two centuries arguing on the ground that he laid out.

And while his exact method of doubt is not practical for normal life, the need to doubt, to question not only what there is, but how we can know or be so sure about what there is, is vital in a world where a great many “gods” are trying to convince us, or deceive us, every single day. 

Your turn

Here are some questions to increase your understanding and help you remember any new vocabulary. You can answer them with a friend or tutor, or write the answers down. Try to use any new vocabulary in your answers.

• Does thought actually require a thinker? If not, perhaps Descartes’ only certainty is that thought is occurring, not that there is an “I” creating this thought. Several philosophers have argued this, but what do you think?
  
• Descartes wanted certainty beyond a shadow of a doubt. Is that a reasonable standard to ask for? Or is it perhaps too restrictive? Why?
  
• How could you utilise doubt and scepticism in your own life to test your own beliefs and to strengthen them?

Did you find this level of English too easy? Then congratulations! You can try engaging with native-level content or check out some of my other articles.

About the author
Joe Tuckwell is an English teacher and the creator of English with Ideas.

If you wish to learn more about Descartes at a harder native level, try these links below:

https://en.wikipedia.org/wiki/Ren%C3%A9_Descartes (Wikipedia, accessible overview)

https://plato.stanford.edu/entries/descartes/ (Stanford Encyclopaedia, in-depth and reliable)

https://www.earlymoderntexts.com/authors/descartes (a wonderful resource for modernised classical texts).

Or find the originals at https://www.gutenberg.org/

(Below) John Anster Fitzgerald, Public domain, via Wikimedia Commons

https://commons.wikimedia.org/wiki/File:Fitzgerald,_The_stuff_that_dreams_are_made_of.jpg