Sect.
III. Of
the Association of Ideas
        
        
        
          18. IT is evident
that there
is a principle of connexion between the 
        different thoughts or ideas
of the
mind, and that, in their appearance 
        to the memory or
imagination, they
introduce each other with a certain 
        degree of method and
regularity.
In our more serious thinking or 
        discourse this is so
observable
that any particular thought, which 
        breaks in upon the regular
tract
or chain of ideas, is immediately 
        remarked and rejected. And
even
in our wildest and most wandering 
        reveries, nay in our very
dreams,
we shall find, if we reflect, that 
        the imagination ran not
altogether
at adventures, but that there was 
        still a connexion upheld
among the
different ideas, which succeeded 
        each other. Were the loosest
and
freest conversation to be 
        transcribed, there would
immediately
be observed something which 
        connected it in all its
transitions.
Or where this is wanting, the 
        person who broke the thread
of discourse
might still inform you, 
        that there had secretly
revolved
in his mind a succession of 
        thought, which had gradually
led
him from the subject of conversation. 
        Among different languages,
even
where we cannot suspect the least 
        connexion or communication,
it is
found, that the words, expressive of 
        ideas, the most compounded,
do yet
nearly correspond to each other: 
        a certain proof that the
simple
ideas, comprehended in the compound 
        ones, were bound together by
some
universal principle, which had an 
        equal influence on all
mankind. 
          19. Though it be
too obvious
to escape observation, that different 
        ideas are connected
together; I
do not find that any philosopher has 
        attempted to enumerate or
class
all the principles of association; a 
        subject, however, that seems
worthy
of curiosity. To me, there 
        appear to be only three
principles
of connexion among ideas, namely, 
        Resemblance, Contiguity in
time
or place, and Cause or Effect. 
          That these
principles serve
to connect ideas will not, I believe, be 
        much doubted. A picture
naturally
leads our thoughts to the original:* 
        the mention of one apartment
in
a building naturally introduces an 
        enquiry or discourse
concerning
the others:*(2) and if we think of a 
        wound, we can scarcely
forbear reflecting
on the pain which follows 
        it.*(3) But that this
enumeration
is complete, and that there are no 
        other principles of
association
except these, may be difficult to 
        prove to the satisfaction of
the
reader, or even to a man's own 
        satisfaction. All we can do,
in
such cases, is to run over several 
        instances, and examine
carefully
the principle which binds the 
        different thoughts to each
other,
never stopping till we render the 
        principle as general as
possible.*(4)
The more instances we examine, 
        and the more care we employ,
the
more assurance shall we acquire, that 
        the enumeration, which we
form from
the whole, is complete and entire. 
  
          * Resemblance.
        
          *(2) Contiguity.
        
          *(3) Cause and
effect. 
          *(4) For instance
Contrast
or Contrariety is also a connexion 
        among Ideas: but it may,
perhaps,
be considered as a mixture of 
        Causation and Resemblance.
Where
two objects are contrary, the one 
        destroys the other; that is,
the
cause of its annihilation, and the 
        idea of the annihilation of
an object,
implies the idea of its 
        former existence.