Amazingly (to me), some scholars (like philosopher Daniel Dennett) deny that consciousness exists.
Philosopher Galen Strawson calls this "the silliest claim ever made." ("The Consciousness Deniers")
What is consciousness? It's like this. I now feel a pain in my shoulder. That is, I am now conscious of a feeling of pain in my shoulder.
Conscious experience is the subjective character of experience. It is the "what-is-it-like" of experience. What is it like, as Thomas Nagel famously asked, to be a bat?
Why might someone deny consciousness? They might, if they are a naturalist. That is, if they believe reality is physical, and nothing more.
Strawson calls those who deny consciousness exists the "Deniers." He writes: "One of the strangest things the Deniers say is that although it seems that there is conscious experience, there isn’t really any conscious experience: the seeming is, in fact, an illusion."
But this presents a problem. "The trouble with this is that any such illusion is already and necessarily an actual instance of the thing said to be an illusion."
Strawson's entire article is wonderful, funny, and sensible. Anyone interested in the very important discussion over consciousness, free will, the self, etc., should read this contribution.
Dennett's response to Strawson, plus Strawson's reply, is here.
Finally, Strawson writes:
Dennett's "position was summarized in an interview in The New York Times: “The elusive subjective conscious experience—the redness of red, the painfulness of pain—that philosophers call qualia? Sheer illusion.” If he’s right, no one has ever really suffered, in spite of agonizing diseases, mental illness, murder, rape, famine, slavery, bereavement, torture, and genocide. And no one has ever caused anyone else pain.
This is the Great Silliness. We must hope that it doesn’t spread outside the academy, or convince some future information technologist or roboticist who has great power over our lives." (Ib., emphasis mine)
See J. P. Moreland, Consciousness and the Existence of God: A Theistic Argument