neither the infallible nor the sole causes of an union among ideas. They
are not the infallible causes. For one may fix his attention during
Sometime on any one object without looking farther. They are not the sole
causes. For the thought has evidently a very irregular motion in running
along its objects, and may leap from the heavens to the earth, from one
end of the creation to the other, without any certain method or order.
But though I allow this weakness in these three relations, and this
irregularity in the imagination; yet I assert that the only general
principles, which associate ideas, are resemblance, contiguity and
causation.

There is indeed a principle of union among ideas, which at first sight
may be esteemed different from any of these, but will be found at the
bottom to depend on the same origin. When every individual of any species
of objects is found by experience to be constantly united with an
individual of another species, the appearance of any new individual of
either species naturally conveys the thought to its usual attendant. Thus
because such a particular idea is commonly annexed to such a particular
word, nothing is required but the hearing of that word to produce the
correspondent idea; and it will scarce be possible for the mind, by its
utmost efforts, to prevent that transition. In this case it is not
absolutely necessary, that upon hearing such a particular sound we
should reflect on any past experience, and consider what idea has been
usually connected with the sound. The imagination of itself supplies the
place of this reflection, and is so accustomed to pass from the word to
the idea, that it interposes not a moment's delay betwixt the hearing of
the one, and the conception of the other.

But though I acknowledge this to be a true principle of association among
ideas, I assert it to be the very same with that betwixt the ideas of