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Dream argument

The dream argument is the assertion that the act of dreaming provides such intuitive evidence that it cannot be distinguished from that which our senses provide to us in the waking state, and that, for this reason, we cannot fully trust the senses we use to distinguish reality from illusion. As a result, any experience that comes out of our senses should at least be carefully examined and rigorously tested to determine if it really refers to “reality.”

Visul vieții, Michelangelo(The Dream of Life, by unknown Mannerist painter, ca. 1533)


When people dream, they usually don’t realize that they are dreaming. This has led philosophers to wonder if we are not constantly dreaming, instead of being in waking reality as we believe; or at least, to notice that we cannot be sure that we are not dreaming. This is a skeptical strategy.

In ancient times

This hypothesis is formulated for the first time it seems in Greek Antiquity by Plato and Aristotle, with the objective of refuting the supposed empiricism of Heraclitus and Protagoras. Indeed, according to the reconstruction of their arguments by Plato then by his disciple Aristotle, Heraclitus would support the moving character of all things and Protagoras the impossibility of knowing a thing in an absolute way, because of the relativity of the sensation of each man. Therefore, the critique of sensation as the sole source of knowledge via the dream argument allows Plato and Aristotle to assert a “rationalist” position, that is to say admitting the possibility of knowing the fixed essence of things beyond the sensitive variations which are the object only of opinions and not of science.

The argument is used at the same time in Chinese philosophy by Tchouang-tse: it is the thought experiment of the butterfly’s dream. The philosopher identifies with a butterfly, not knowing if he is Chuang-tse who dreamed of being a butterfly or if he is a butterfly who dreams of being Chuang-tzu, after his supposed awakening.

Skeptical philosophers will take up the argument (Aenesidemus, fourth trope), with a goal quite different from Plato and Aristotle: it is a strategy aimed at defeating all certainty and all definitive knowledge. The argument thus takes place in tropes which seek relativism and the suspension of judgment. Seneca speaks of the “Divinity who envelops in a long deceptive dream” the “poor souls without consistency”, with the aim of enhancing the real goods which are interior. The argument will be reused by Pascal in a moralistic and apologetic sense.


Cartesian critique of sensation

The dream argument has received notable attention in modern philosophy from René Descartes. According to Adrien Baillet, Descartes had in his youth, in 1619, three dreams which decided his philosophical and scientific vocation. In the third dream in particular, Descartes dreamed of a dictionary of poetry and “what is singular to notice is that, doubting whether what he had just seen was a dream or a vision, he not only decided in sleeping that it was a dream, but he still interpreted it before sleep left him”. Descartes interpreted his own dream as the vision of the spirit of truth, which communicated to him the enthusiastic desire to develop the sciences, a desire which will fall soon after his awakening only to return later. Descartes will keep from these dreams an esteem for the poetic form. Grimaldi notes Descartes’ taste for the simulation of reality from this time on.

Descartes uses the argument of the dream in the Meditations on First Philosophy to exhibit the uncertain character of the information given by the senses. The argument thus takes place in a series of thought experiments: optical illusions, then madness and the evil genius. Descartes emphasizes the realistic nature of the dream, and the difficulty of distinguishing it from sensation in the waking state: “How many times have I dreamed, at night, that I was in this place, that I was dressed, that I was near the fire, although I was quite naked in my bed?“ But this argument, if it is relevant to question sensitive knowledge, does not make it possible to waver mathematical knowledge, which is why Descartes seeks others, to lead to the evil genius. Descartes ends up giving himself the refutation of this argument of the dream: “our memory can never link and join our dreams to each other and with all the rest of our life, as it is in the habit of joining things that come to us while awake.“ It is the continuity that will allow us to distinguish the dream from the day before. Descartes will maintain in his correspondence with Elisabeth of Bohemia that it is possible to control his dreams, through habituation and working on his emotions: “thus I can say that my dreams never represent anything unfortunate to me, and no doubt that we have a great advantage in having long accustomed ourselves to not having sad thoughts.“

Pascalian apologetics

This same continuity serves to distinguish dream from reality in Pascal, who uses the dream argument to make us doubt the value of the goods of this world. He compares a king who dreams every night that he is a craftsman, and a craftsman who dreams every night that he is a king: the psychological effects would be according to the philosopher similar, thus providing the same amount of joy and sorrow in one and the other case. The same goes for nightmares and creepy ghost dreams. This would show that the illusion of happiness and earthly happiness are identical, and naively taken for real happiness by men. The argument then takes on a moral tone and skepticism is here at the service of the Christian religion: it is a question of demonstrating the vanity of happiness obtained by earthly means, for the benefit of salvation and faith in celestial existence. Pascal makes an allusion to the play by Calderón, whose title he cites: La vie est un songe (“a little less inconstant”).

In contemporary thought

After Descartes and Pascal, Hilary Putnam, through her “brain in the tank” thought experiment, takes up the dream argument to test skepticism again. The principle will be repeated in the film Matrix. The dream argument is reinterpreted from simulated reality and the simulation hypothesis.

The dream is also related to hallucination by Sigmund Freud: it uses defense mechanisms that modify the perception of reality (such as displacement).

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