Hume’s Radical Empiricism: on the origin of ideas and the semantic test
I. HUME ON THE ORIGIN OF IDEAS
Hume divides all the mind’s perceptions into two categories:
impressions and ideas. Impressions are immediate sensory experiences:
they are forceful and vivacious, such that we can’t be mistaken about their
nature. Ideas are derivative, secondary perceptions: they are weaker and
paler, and thereby subject to manipulation by the imagination.
The Copy Principle: “all our simple ideas…are deriv’d from simple
impressions.”
But if all ideas are copies of impressions, how come we can have the idea of
“a solid gold mountain” even though we’ve never had the impression of
one? How about the idea of a “unicorn”, or of “mermaid”?
For Hume, these are examples of complex ideas, which are made by
compounding simple ideas. We have had experiences (i.e., impressions) of
“gold” and of “mountain”. These simple impressions were copied as ideas.
Once copied as ideas, our imagination is able to manipulate them, combining
and separating them at will. That’s how we come up with fictional complex
ideas like “gold mountain” even though we’ve never experienced one. The
components of the complex idea must be derived from previous impressions
that we have had.
II. HUME’S SEMANTIC TEST
From An Enquiry concerning Human Understanding:
“Here, therefore, is a proposition, which not only seems, in itself, simple and
intelligible; but, if a proper use were made of it, might render every dispute
equally intelligible, and banish all that jargon, which has so long taken
possession of metaphysical reasonings, and drawn disgrace upon them. All
ideas, especially abstract ones, are naturally faint and obscure: the mind has
but a slender hold of them: they are apt to be confounded with other
resembling ideas; and when we have often employed any term, though
without a distinct meaning, we are apt to imagine it has a determinate idea
annexed to it. On the contrary, all impressions, that is, all sensations, either
outward or inward, are strong and determined: nor is it easy to fall into any
error or mistake with regard to them. When we entertain, therefore, any
suspicion that a philosophical term is employed without any meaning or idea
(as is but too frequent), we need but enquire, from what impression is that
supposed idea derived? And if it be impossible to assign any, this will serve
to confirm our suspicion. By bringing ideas into so clear a light we may
reasonably hope to remove all dispute, which may arise concerning their
nature and reality.”
Hume’s method for telling the difference between “metaphysical jargon”
and meaningful claims:
Can the idea be traced back to sensory experience? Is the idea derived
from sensory experience? “From what impression is the supposed idea
derived?”
If we can answer these questions, then the idea has “empirical
content”, and any disputes can, at least in theory, be resolved by established
methods.
If it is impossible to answer these questions, then the supposed idea or
claim is meaningless (literally “senseless”). Disputes concerning such
meaningless ideas are so much sound and fury signifying nothing.
Obviously, we can make no claims to know what cannot even be understood.