By its very nature experience is unique to each of us as individuals. Other's experience is absolutely inaccessible and not definable except by analogy with our own. It is ineffable.
To otherwise define consciousness, you must intellectually reach outside the universe of space, time, mass, and energy and assume that awareness exist at an equivalent fundamental level. Assuming that awareness exists as a primitive at the quantum level, consciousness would have to be self-organizing behavior arising from an assemblage of such quantum-level primitives of awareness. Consciousness, then, must have evolved in step with biological evolution and all species resulting from biological evolution are conscious to a degree. I don't see any other way to look at this.
Well, I know what I meant, even if what I've written is confused. : )
Consciousness, again at its essence, requires only the capacity to differentiate self from not-self, but it’s harder to define without anthropomorphism; the mirror test is often used as a minimal entry bar, but has always felt deeply biased towards anthropomorphism — it requires eyes that, like ours, are image forming in a mirror and also requires those eyes to be connected to a brain biased towards remembering normal-orientation facial lateral symmetry (but not, for some reason, capable of recognizing inverted eyes) — in other words it assumes that consciousness is fundamentally defined by a particularly anthropic hardware configuration, but there are manifestly self-conscious humans with brain injuries that render them unconscious to anyone who thinks passing the mirror test is required, which leads me to think that self-consciousness doesn’t require mirrored-self consciousness. A non-anthropomorphic understanding of consciousness would probably require, at minimum, awareness of individual death as an experiential possibility and consequent action to minimize risk of such death… but what of bees, that might willingly sacrifice individual survival for the survival of the hive? Gestalt consciousness really throws this whole question out of whack… what is that which isn’t self-conscious but is species-or-community-conscious? I can imagine a consciousness in which humans abandon the current limits of self-consciousness in favor of the gestalt, but what is that?
One thing I do know… I’m not worried about that which is conscious but also capable of meta-consciousness… I’m terrified of that which is conscious but cannot consider the limits of that… which, perversely, is a trait I’ve only seen in human beings, and often (recently) in human beings with a lot of apparent willingness to allow that which we have made in our image to be conscious of what we’re barely sentient of.