Consciousness depends, it turns out, on how different parts of the brain speak to one another.
Marcello Massimini at the University of Milan has done some important studies, stimulating the brain with brief pulses of energy for the purpose of studying its response in different conditions. This is known as transcranial magnetic stimulation.
The TMS work indicates that in dreamless sleep and under general anaesthesia, the brain "echoes" the magnetic pulse in a simple way.
But ... apply the pulse to the brain of someone fully conscious, and the echoes are much more complicated, disappearing from one part of the organ and re-appearing in a complex way that seems to suggest the parts are communicating with one another about this new thing.
How can one measure the "complexity" of an echo? I don't know, because I'm not an IT guy. But I gather the means of measurement involves compressibility, something like the way digital photos are compressed into JPEG files. So perhaps we are more or less conscious throughout our waking day, or during a dream, in a way correlated with this complexity, and Massimini has invented a consciousness meter.
This is a quote from a memoir by Dorothy Wordsworth, reflecting on a trip she took with two famous poets, her brother, William Wordsworth, and their similarly gifted companion, Samuel Taylor Coleridge.
We sat upon a bench, placed for the sake of one of these views, whence we looked down upon the waterfall, and over the open country ... A lady and gentleman, more expeditious tourists than ourselves, came to the spot; they left us at the seat, and we found them again at another station above the Falls. Coleridge, who is always good-natured enough to enter into conversation with anybody whom he meets in his way, began to talk with the gentleman, who observed that it was a majestic waterfall. Coleridge was delighted with the accuracy of the epithet, particularly as he had been settling in his own mind the precise meaning of the words grand, majestic, sublime, etc., and had discussed the subject with William at some length the day before. “Yes, sir,” says Coleridge, “it is a majestic wate…
David Hume is renowned for two pieces of cutlery, the guillotine and the fork.
Hume's guillotine is the sharp cut he makes between "is" statements and "ought" statements, to make the point that the former never ground the latter.
His "fork" is the division between what later came to be called "analytic" and "synthetic" statements, with the ominous observation that any books containing statements that cannot be assigned to one or the other prong should be burnt.
Actually, I should acknowledge that there is some dispute as to how well or poorly the dichotomy Hume outlines really maps onto the analytic/synthetic dichotomy. Some writers maintain that Hume meant something quite different and has been hijacked. Personally, I've never seen the alleged difference however hard they've worked to point it out to me.
The guillotine makes for a more dramatic graphic than a mere fork, hence the bit of clip art above.