In his first meditation Descartes says that he cannot distinguish a state where he is dreaming from a vigil state. This gives him one reason to at least put in doubt the direct corporeal experience of the senses.

My doubt is very simple. If he cannot distinguish this two states, how can he even formulate this distinction?

I was trying to imagine how i can come up with a concept of Vigil if a cant really distinguish it from a dream.

  • The Meditator: "Whatever I have up till now accepted as most true I have acquired either from the senses or through the senses. But from time to time I have found that the senses deceive, and it is prudent never to trust completely those who have deceived us even once. (vii:18)" Thus, he applies the maxim that if a certain source (e.g. experience) has ever been found untrustworthy or deceitful, the purported knowledge issuing from that source are dubious. Mar 22, 2023 at 11:43
  • "How often, asleep at night, am I convinced of just such familiar events – that I am here in my dressing-gown, sitting by the fire – when... (vii:19)" If we cannot have a reliable criteria to ascertain if we are awake or asleep and dreaming, again we cannot rely on purported sesnsory experience. Mar 22, 2023 at 11:45
  • My doubt is exactly about one frase "Quae dum cogito attentius, tam plane video nunquam certis indiciis vigiliam a fommo posse distingui" (line 17 - 21). My humble translation "when i think more carefully, i see in a more manifest way that the vigil state NEVER can be distinguished from a sleed state by a certain fact". Well, if a NEVER can distinguish one state from another, HOW i can even say that exist something called vigil state?
    – LAU
    Mar 22, 2023 at 13:24
  • By "vigil", do you mean "awake"? Mar 22, 2023 at 15:54
  • Yes. My natural language is not english, so maybe i'm not being precise in this language, but yes, vigil meaning awake.
    – LAU
    Mar 22, 2023 at 16:23

2 Answers 2


One way to answer your question is to think about how you (and, probably, almost everyone else) learnt to distinguish dream from waking in real life.

Many parents will have experienced being woken up by their small child rushing into the bedroom, very upset because there are wolves all round the house, or some similar problem. Parents then persuade the child to recognize that s/he is awake now and that there are no wolves around the house. Sometimes this goes on for a while, but eventually we all learn the difference.

We often think we can distinguish dream for sleep while we are asleep but that isn't true. While we are asleep, we are incapable of recognizing a fantasy. That's what it means to be asleep. So there is no cue that will tell us we are awake. We realize we were dreaming when we wake up with impossible memories and recall what a dream is.

There are many complications around this in practice, but the principle is clear.

Descartes is right to think that there is no cue that will tell us we are dreaming while we are dreaming. After all, in a dream, everything is deceptive. If there were a cue that told you whether you were dreaming, it would be unreliable, because you were dreaming.

What Descartes misses is the point that he can wake up, and that's how he knows (later on) that he was dreaming. It is the overall coherence of our lives that tells us we are awake and the incoherence of dreams with our lives is what tells us they are dreams. But we can't recognize the difference while we are asleep and unconscious.

  • What about lucid dreams? Mar 22, 2023 at 16:00
  • I wondered if anyone would ask about that. Are you suggesting that lucid dreams provide Descartes with a criterion to decide whether he is dreaming or not? The dreamer, so far as I understand the phenomenon, does not realize or decide that they are dreaming. The piece you linked to just says "becomes aware". That's rather different. The context suggests that Descartes has in mind asking and answering the question while he is asleep. Then there might be some answer to the question "How do you know?" Is that possible? I don't know.
    – Ludwig V
    Mar 22, 2023 at 16:42
  • I don't understand what distinction you are drawing between "realize or decide" and "becomes aware". Regardless of how you describe it, a dreaming person can know that they are dreaming. Mar 22, 2023 at 17:45
  • There are, of course, philosophical issues about the epistemological status all reports of dreams given that we know they are illusions and that the dreamer is asleep while they are reported as occurring. They cannot be verified or falsified, even in the ways that first person reports of waking experiences can be confirmed or dismissed. If they are "expressions" rather than reports, as is the case with waking experiences, then they are neither true nor false. So then it is possible to suggest that the impression of control may be an illusion - just a part of the dream.
    – Ludwig V
    Mar 22, 2023 at 17:52
  • In the comparable cases of people reporting waking up during operations, it is possible to take steps to ensure that they don't happen, because the anaesthetist can identify the symptoms. That doesn't seem to be possible in the case of lucid dreams. So I'm not sure what to make of them. I won't say any more because this is off topic.
    – Ludwig V
    Mar 22, 2023 at 17:52

Your waking life constitutes a coherent whole; your dreaming life does not. when you go to sleep, you typically wake up in the same place, with the same people around, in the same situation as when you went to sleep. Your experience continues more or less where it left off, in ways that are predictable and coherent. Furthermore, there are predictable and coherent rules of what can and can't happen in waking life. Things don't suddenly appear and disappear, the world doesn't suddenly and inexplicably change around you, and you can't fly.

In all of these characteristics, dreams are otherwise. The dreams that you have over your life don't form a single coherent world, but a scattered hodgepodge of many different worlds, none of which individually forms a reliable and predictable stage on which to act.

If you had a series of dreams that work like real life, where every time you started this particular dream, it left off where the previous ended, where the situation usually changed only gradually, in a regular and predictable way like real life, a dream that over years formed a progressing coherent world like waking life, with real consequences to your actions, then you would have reason to believe that in that dream you are accessing another world similar to the waking world. There have been fantasy stories that work with this premise.

  • That all makes sense. What is difficult, though, is to stop there. We cannot resist trying to make sense of the phenomenon, especially to disentangle what is real and true and what is fantasy and deception. That's not a bad thing, in itself. But we don't seem to have made much progress yet.
    – Ludwig V
    Mar 23, 2023 at 5:57

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