Cogito, ergo sum1, translated from Latin: I think, therefore I am. Perhaps the most famous words uttered in philosophy, and the cradle of the problem of Solipsism. In Discourse on Method and the Meditations2, philosopher René Descartes proposes the Evil Demon hypothesis

Evil Demon Hypothesis: A demon of utmost power and cunningness has employed its energy to deceive you. All external things, including other humans, that you experience are merely delusions devised by it to obscure your judgment.

While an extreme example, one can’t deny its possibility. If true, that would imply that you are the only conscious creature in the world, apart from the demon, and others are mere puppets, automata at its hands. Constructed more rigorously, the Problem of Other Minds3 addresses the question – Do other conscious minds, apart from myself, exist? A modified argument is given below, based on Wittgenstein’s Private Language Argument4, that argues for the irrelevance of solipsistic concerns.

Private Language Argument

Philosophical Investigations5, perhaps Wittgenstein’s most important work, introduces the concept of private language. Imagine a person with a language the can only be understood by herself. Note that a language that is only understood by one person, say a dying language with one last speaker, in principle can be learned. Therefore, it is not a private language.

The individual associates some recurrent sensation with the symbol S, marked on paper when the sensation occurs. It’s required that this sensation cannot be defined with other terms, for instance “the feeling of waking up at 4 am”, for that would make this language public, as it can be understood by others. One can only use an ostensive definition here, conveying the meaning of terms by pointing out examples. For her sensation points to the symbol S in an ostensive fashion.

Wittgenstein argues for the incoherence of such a language, by its inherent tautological6 nature, devoiding it of any possible meaning. This development is made possible through Frege’s Sense and Reference7, and later Wittgenstein’s Tractatus logico-philosophicus8. Thus a language with meaning must be public. This proves the existence of other entities that can understand and communicate with the individual. Leaving us with a singular question from the sceptic – How can we assert that other such entities are conscious? Underneath lies the argument for why such a contention is irrelevant.

Argument from Tautology

How does an individual realize that they are conscious? Perception. Call such knowledge of individual consciousness Consciousness-i. There’s no denying that one perceives consciousness in other humans, relative to animals and other creatures. Even if it’s claimed to be pseudo-consciousness, term that Consciousness-o.

The argument arises from the contention that one can’t truly know whether Consciousness-i and Consciousness-o are the same. Such an argument remains incoherent, as it is tautological and hence meaningless. Consciousness-i and Consciousness-o can never be the same by definition.

For if Consciousness-o, representing the perception of consciousness in other people, was equal to Consciousness-i, representing the perception of individual consciousness, they would be perceiving the same thing. In other words, other people and the individual would be the same, contradicting the initial conditions.


The thesis relies upon utilizing the Private Language Argument to prove the existence of public experiences, sensations, and modes of communication. Then asserting the tautological notion of questioning those public agents on the non-exhibitive property of individual consciousness, one that can only be perceived by the individual.

  1. Wikimedia Foundation. (2023, February 27). Cogito, ergo sum. Wikipedia. Retrieved March 10, 2023, from,_ergo_sum
  2. Descartes René, Veitch, J., & Descartes René. (2018). Discourse on Method and the Meditations. Adansonia Press.
  3. Avramides, A. (2019, May 2). Other Minds. Stanford Encyclopedia of Philosophy. Retrieved March 10, 2023, from
  4. Candlish, S., & Wrisley, G. (2019, July 30). Private language. Stanford Encyclopedia of Philosophy. Retrieved March 10, 2023, from
  5. Wittgenstein, L. (1992). Philosophical Investigations. Blackwell.
  6. true by virtue of its logical form alone, exhibits redundancy in propositions. Example: He is healthy or he is not healthy.
  7. Frege, G. (1948). Sense and Reference. The Philosophical Review57(3), 209–230.
  8. Wittgenstein, Ludwig, 1889-1951. (1933). Tractatus logico-philosophicus. [Reprinted, with a few corrections] New York :Harcourt, Brace

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