Thursday, October 30, 2014

How Does Hume Separate Sense Impressions and Hallucinations?

Back in 1839, philosopher David Hume couldn't hold back any longer, so he sallied forth, at the grand old age of eighteen, to write his Treatise of Human Nature. Why not? The Scots are notoriously dour and flinty, and certainly exposed at a young age to the reality of a long winter, so a young lad raised on haggis and mutton ought to have a clear and unclouded mind uninflamed by the fripperies of London and its Sassenach coffee-houses.

He starts out, as any philosopher must, by clearing the ground. In young David's case, he tells us the difference between "impression" and "idea." The difference between the two, he writes, consists in the "degrees of force and liveliness, with which they strike upon the mind, and make their way into our thought or consciousness."

There should be no problem in discriminating between the two, he writes, even though "in sleep, in a fever, in madness... our ideas may approach our impressions."

Oh yeah?  Just how then do we do it? How close can an hallucination approach us in force and vivacity before we dignify it with the rank of "impression?" Other than the classic professorial put-down that it's obvious?

In fact, of course, scholars and wrangled about this forever, because it's a rather glaring aporia (that's Greek for no way through) in Hume's system.

Here's one chappie's effort. He says that there's a difference between a representation and an actual presentation, or experience. You can have an idea of the Acropolis, but until you've actually been there and seen it --  well, it's just a hallucination.

Hume himself deals with the problem later in Book One of the Treatise. Sure, he says, a "lively imagination very often degenerates into madness or folly" as does any "chimera of the brain." But you and I are able to differentiate such phantasms and similar poetical effusions. The fact is that we can tell the difference between the fiction and the real, he asserts.

Well yes. That's the definition of sanity, I reckon. You can tell the difference between the voices in your head, however forceful and vivacious, and the relentless reality out there in the world that eventually turns our hair gray. Anything else is madness.

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