Elements of the philosophy of the human mind. By Dugald Stewart. Rev. and abridged, with critical and explanatory notes, for the use of colleges and schools. By Francis Bowen ...

THE INFLUENCE OF CASUAL ASSOCIATIONS. 209.iT st, by blending together in our apprehensions things which
are really distinct in their nature; so as to introduce perplexity
and error into every process of reasoning in which they are
involved.
Secondly, by misleading us in those anticipations of the future from the past, which our constitution disposes us to form,
andc which are the great foundation of our conduct in life.
Thirdly, by connecting in the mind erroneous opinions with
truths which irresistibly command our assent, and which we feel
to be of importance to human happiness.
A short illustration of these remarks will throw light on the
origin of various prejudices; and may, perhaps, suggest some
practical hints with respect to the conduct of the understanding.
1. Association often blends together things which are really
distinct.- I formerly had occasion to mention several instances
of very intimate associations formed between two ideas which
have no necessary connection with each other. One of the most
remarkable is, that which exists in every person's mind between
the notions of color and of extension. The former of these
words expresses (at least in the sense in which we commonly
employ it) a sensation in the mind; the latter denotes a qualiky
of an external object; so that there is, in fact, no more connection
between the two notions than between those of pain and of
solidity; and yet, in consequence of our always perceiving
tonian theory of the tides is not the less certain, that some apparent exceptions occur to it, of which it is not easy (in consequence of our imperfect
knowledge of the local circumstances by which, in particular cases, the
effect is modified) to give a satisfactory explanation.
Of the solutions suggested by M. Prdvost, the first coincides most nearly
with my own opinion; and it approaches to what I have hinted (in page
202 of this work) concerning the seeming exceptions to my doctrine, which
may occur in those cases where sleep is partial. A strong confirmation of
it, undoubtedly, may be derived fiom the experience of those persons,
(several of whom I have happened to meet with,) who never recollect to
have dreamed, excepting when the soundness of their sleep was disturbed
by some derangement in their general health, or by some accident which
excited a bodily sensation.
Dr. Reid has, with great truth, observed, that Des Cartes' reasonings
against the existence of the secondary qualities of matter, owe all their
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