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)
Upanishads are earlier recorded arguments on consciousness and other internal phenomena.
You can browse various translations of these scriptures in English.

P.S. It seems any reference to Indian Philosophies are getting negative voting on this site. 

Edit: Aitareya Upanisad from the rigveda which is older than any given scripture.

An English translation of one of the Sloka:

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> III-i-3: This One is (the inferior) Brahman; this is Indra, this is Prajapati; this is all these gods; and this is these five elements, viz. earth, air, space, water, fire; and this is all these (big creatures), together with the small ones, that are the procreators of others and referable in pairs – to wit, those that are born of eggs, of wombs, of moisture of the earth, viz. horses, cattle, men, elephants, and all the creatures that there are which move or fly and those which do not move. **All these have Consciousness as the giver of their reality; all these are impelled by Consciousness; the universe has Consciousness as its eye and Consciousness is its end. Consciousness is Brahman.** 
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Here you guys can find numerous iterations of consciousness word.

Other Upanishad from Rigveda:

Aitareya 

Atmabodha 

Kaushitaki 

Mudgala 

Nirvana 

Nadabindu 

Akshamaya 

Tripura 

Bahvruka

Saubhagyalakshmi