Neurosurgeon Michael Egnor offers this definition by way of explaining that there is one sense in which consciousness IS an illusion: We are not aware of our consciousness; only of its objects.
I believe that the most satisfactory definition of consciousness is the intentional power of the mind — the ability of thought to be “about” something. Consciousness is always directed to an object, whether that object is physical, emotional, or conceptual. If there is no “aboutness,” there is no consciousness.
All intentionality entails two things: the process by which (1) we think about something, and the thing about which (2) we think. When I perceive a tree, I am perceiving (1) a tree (2). When I think about justice, I am contemplating (1) justice (2).
This understanding of the mind — that thought involves both that of which we think (2) and that by which we think (1) dates back to Aristotle (384–322 BCE). It was a cornerstone of Thomas Aquinas’s (1225–1274) philosophy of mind.
St. Thomas, following Aristotle, observed that it is only the objects of thought that we are aware of. We are never aware of the process of thought. Thus, sensation, perception, memory, judgment, understanding, etc., are unconscious processes. They are the processes by which we sense bodily feelings, perceive objects, remember faces,
judge opinions, and understand concepts. But it is the feelings, objects, faces, opinions, and concepts themselves of which we are conscious. We are never conscious of the sensations, perceptions, etc., by which we are conscious of these objects. Michael Egnor, “In one sense, consciousness IS an illusion…” at Mind Matters
Dr. Egnor thinks that philosopher Peter Carruthers probably means something like that when he writes about “The Illusion of Conscious Thought.”s Of course, in the age of the thinking electron, the conscious coffee mug, and human consciousness as an illusion, the philosopher would be wise to make quite clear that he, by contrast, is trying to stick to observable reality.
Also by Michael Egnor: Does Your Brain Construct Your Conscious Reality? Part I A reply to computational neuroscientist Anil Seth’s recent TED talk
and
Does Your Brain Construct Your Conscious Reality? Part II In a word, no. Your brain doesn’t “think”; YOU think, using your brain
See also: Panpsychism: You are conscious but so is your coffee mug