born blind, he may acquire speech to its fullest
extent without having any Ideas, which therefore cannot be considered
the necessary instruments of Thought. Thus, the presumed mutual
intercourse, and reciprocal correspondence between Ideas and words is a
very disputable conclusion.

When the Idea or phantasm that is connected with visual perception
appears, in consequence of the word being mentioned (which by
commutation is its substitute), the presentation is immediate. He who
has visited and attentively noted interesting scenes, mountainous
districts, cataracts or prospects, when they are mentioned, will have
their phantasms or pictured images occur to him, and he will be aware of
them, like the intrusion of a sudden flash. From this phenomenon the
generally received opinion of the _rapidity_ of _Thought_ may in all
probability have originated.

All popular and settled notions, however unfounded, like prejudices
early imbibed, are with difficulty eradicated. Among these may be
instanced the dictum of the astonishing rapidity of Thought, which is
almost proverbial, and generally believed: even Mr. TOOKE, Vol. I., p.
28, conforms to this established maxim. "Words have been called
_winged_: and they well deserve that name, when their abbreviations are
compared with the progress which speech could make without these
inventions; but when compared with the _rapidity_ of _thought_, they
have not the smallest claim to that title." By calculation, the progress
of light from the sun and other luminaries is said to be ascertained;
and likewise the rate at which sound travels: but hitherto no
contrivance has been fabricated to estimate the rapidity of thought. If
the succession of our thoughts should be more rapid than they can be
distinctly apprehended, confusion must ensue, and their rapidity would
render them useless. Our perceptions are regulated by the same law. If
the prismatic colours be painted on a surface which is revolved with
great rapidity, the individual colours will not be apparent. The
succession of sounds to a definite number, may be severally
distinguished, in a certain interval: but if the succession be
increased beyond the power of discrimination, they will impress the ear
as one uniform sound. The same principle must regulate our thoughts,
whether they be composed of Ideas or words, or, if it be possible, of
both jumbled together. It does not appear that our thoughts for any
useful purpose, which must imply