Question: I have seen the following argument in several places:

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> Consciousness cannot be an illusion, and it surely exists.
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> An illusion is perceiving something to be true when this something is not actually the case. "Perceiving" and "being conscious of" can be taken to be synonymous, so saying that consciousness is an illusion is a contradiction.
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The argument is very strong as it relies on semantics.

**What is the first written philosophical account of this argument?**

Answer: 
1) Taken your question literally: One does not need to argue that consciousness exists. Everybody when awake is conscious and experiences consciousness. 

One can discuss whether every perception is a conscious perception. Because we know that humans can also be triggered by unconscious stimuli. This kind of stimulation is used by marketing mechanisms or by priming, applied in an experimental context of cognitive psychology.

2) Hence the question is not, whether consciousness exists. The questions are:

* How to define conscious mental processes and how to establish the border to unconscious processes?
* Why are some mental processes conscious while others are not? What is the function of conscious processes?

As an introduction I recommend *Koch, Christof: Consciousness - Confessions of a Romantic Reductionist.* (2012). Chapter III reviews some definitions of conscious processes, taken from different view points. 

Whether a person is conscious or not and to which degree he is conscious can be derived from its behaviour. That’s a method used by paramedics using a checklist. 

A more refined criterion to decide about the conscious state of a person is to check the activity of the neocortex and the thalamus. 

A more philosophical definition of being conscious is to register how things seem to us (qualia). 

In any case, conscious mental processes are restricted to the neocortex.

3) An early classification of states of consciousness is given by the Mandukya Upanishad from the beginning of the common era. The Mandukya Upanishad distinguishes four quarters of atman (= the self):

* Vaisvanara: “situated in the waking state, perceiving what is outside […]” (verse 3)
* Taijasa: “situated in the state of dream, perceiving what is inside […]” (verse 4)
* Prajna: “situated in the state of sleep – deep sleep is when a sleeping man entains no desires or sees no dreams […]” (verse 5)
* “They consider the fourth quarter as perceiving neither what is inside nor what is outside, not even both together; not as a mass of perperceptions […]” (verse 7)
Anaxogoras, of Clyzomanae in Asia Minor, around 500 BC write of *nous* as an ordering force in the cosmos:

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> B12: *Nous* is unlimited and self-ruling and has been mixed with no thing; but is alone itself, by itself ... and *nous* has control over all things that have soul, both the larger and the smaller; and *nous* controlled the whole revolution, so that it started to revolve in the beginning.
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Roughly a century earlier, in Miletus, Thales had supposed (reported by Aristotle in *On the Soul*):

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> all things have souls
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In the scriptural corpus of Vedantic Philosophy, the [principal Upanishads](https://en.m.wikipedia.org/wiki/Muktik%C4%81) have a composition date around the turn of the 1st milleneum BCE; the *Eesha Upanishad*, has:

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> The Self is one. Unmoving, it is swifter than the mind. The senses lag, but Self runs ahead. Unmoving it outruns pursuit. Out of Self comes the breath that is the life of all things.
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and

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> The Self is everywhere, without a body, without a shape, whole, pure, wise, all-knowing, far-shining, self-depending, all transcending; it assigns to every period, it's proper duty.
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The Self, is sometimes translated as Consciousness; earlier translations had used soul, which had distinctly Christian overtones - which is possibly why Yeats opted for Self in the collaborative translation, excerpted above; (and possibly, the same artifact of translation is apparent in the translations of the Greek above).