Hey. Google?
Turiya from the perspective of three states of waking, dreaming and sleeping is another state.
But Turiya in itself is non dual without a second. It is not a state. It is the Atman that is Brahman, unassociated with any second.
Mandukya Upanishad
VII
Turiya is not that which is conscious of the inner (subjective) world, nor that which is conscious of the outer (objective) world, nor that which is conscious of both, nor that which is a mass of consciousness. It is not simple consciousness nor is It unconsciousness. It is unperceived, unrelated, incomprehensible, uninferable, unthinkable and indescribable. The essence of the Consciousness manifesting as the self in the three states, It is the cessation of all phenomena; It is all peace, all bliss and non—dual. This is what is known as the Fourth (Turiya). This is Atman and this has to be realized.
XII
The Fourth (Turiya) is without parts and without relationship; It is the cessation of phenomena; It is all good and non—dual. This AUM is verily Atman. He who knows this merges his self in Atman—yea, he who knows this.
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It is non dual Self that is Brahman.
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If you still have doubt, kindly read from say Ramana Maharshi about the Turiya. Or if you wish I can cite more explanatory material.