. At
first sight, it might seem as if, in the fluidity of these successive
waves, everything is indeterminate. But inspection shows that each wave
has a constitution which can be to some degree explained by the
constitution of the waves just passed away. And this relation of the
wave to its predecessors is expressed by the two fundamental 'laws of
association,' so-called, of which the first is named the Law of
Contiguity, the second that of Similarity.

The _Law of Contiguity_ tells us that objects thought of in the coming
wave are such as in some previous experience were _next_ to the objects
represented in the wave that is passing away. The vanishing objects were
once formerly their neighbors in the mind. When you recite the alphabet
or your prayers, or when the sight of an object reminds you of its name,
or the name reminds you of the object, it is through the law of
contiguity that the terms are suggested to the mind.

The _Law of Similarity_ says that, when contiguity fails to describe
what happens, the coming objects will prove to _resemble_ the going
objects, even though the two were never experienced together before. In
our 'flights of fancy,' this is frequently the case.

If, arresting ourselves in the flow of reverie, we ask the question,
"How came we to be thinking of just this object now?" we can almost
always trace its presence to some previous object which has introduced
it to the mind, according to one or the other of these laws. The entire
routine of our memorized acquisitions, for example, is a consequence of
nothing but the Law of Contiguity. The words of a poem, the formulas of
trigonometry, the facts of history, the properties of material things,
are all known to us as definite systems or groups of objects which
cohere in an order fixed by innumerable iterations, and of which any one
part reminds us of the others. In dry and prosaic minds, almost all the
mental sequences flow along these lines of habitual routine repetition
and suggestion.

In witty, imaginative minds, on the other hand, the routine is broken
through with ease at any moment; and one field of mental objects will
suggest another with which perhaps in the whole history of human
thinking it had never once before been coupled. The link here is usually
some _analogy_ between the objects successively thought of,--an analogy
often so subtle that, although we feel it, we can with difficulty
analyze its ground; as where, for example, we fi