response to Hume’s Treatise, and he followed this up in the 1780s with two
essays on the intellectual and active powers of man. The paradoxical conclu-
sions to which Hume’s investigations led made Reid call in question the basic
principles from which he began, and in particular the system of ideas
common to both the British empiricists and the continental Cartesians:
When we Wnd the gravest philosophers, from Des Cartes down to Bishop Berkeley,
mustering up arguments to prove the existence of a material world, and unable to
Wnd any that will bear examination; when we Wnd Bishop Berkeley and Mr Hume,
the acutest metaphysicians of the age, maintaining that there is no such thing as
matter in the universe—that sun, moon, and stars, the earth which we inhabit,
our own bodies, and those of our friends, are only ideas in our minds, and have no
existence but in thought; when we Wnd the last maintaining that there is neither
body nor mind—nothing in nature but ideas and impressions—that there is no
certainty, nor indeed probability, even in mathematical axioms: I say, when we
consider such extravagancies of many of the most acute writers on this subject,
we may be apt to think the whole to be only a dream of fanciful men, who have
entangled themselves in cobwebs spun our of their own brain.
The whole of recent philosophy, Reid maintains, shows how even the most
intelligent people can go wrong if they start from a false W rst principle.
Reid puts his Wnger accurately on the basic error of Desca rtes and Locke,
arising from the ambiguity of the word ‘idea’. In ordin ary language ‘idea’
means an act of mind; to have an idea of something is to conceive it, to have
a concept of it. But philosophers have given it a diVerent meaning, Reid says,
according to which ‘it does not signify that act of the mind which we call
thought or conception, but some object of thought’. Ideas which are Wrst
introduced as humble images or proxies of things end up by supplanting
what they represent and undermine everything but themselves: ‘Ideas seem
to have something in their nature unfriendly to other existences.’
Ideas in the philosophical sense—postulated intermediaries between the
mind and the world—are, in Reid’s view, mere Wctions. We do of course,
have conceptions of many things, but conceptions are not images, and in
any case it is not conceptions that are the basic building blocks of knowledge,
but propositions. Followers of Locke think that knowledge begins with bare
conceptions (‘simple apprehensions’), which we then put together to form
beliefs and judgements. But that is the wrong way of looking at things.
‘Instead of saying that the belief or knowledge is got by putting together and
comparing the simple apprehensions, we ought rather to say that the simpl e
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