The mental vision by which in Perception we see the unapparent
details---i.e, by which sensations formerly co-existing with the one
now affecting us are reinstated under the form of ideas which REPRESENT
the objects--is a process implied in all Ratiocination, which also
presents an IDEAL SERIES, such as would be a series of sensations, if
the objects themselves were before us. A chain of reasoning is a chain
of inferences: IDEAL presentations of objects and relations not
apparent to Sense, or not presentable to Sense. Could we realise all
the links in this chain, by placing the objects in their actual order
as a VISIBLE series, the reasoning would be a succession of
perceptions. Thus the path of a planet is seen by reason to be an
ellipse. It would be perceived as a fact, if we were in a proper
position and endowed with the requisite means of following the planet
in its course; but not having this power, we are reduced to infer the
unapparent points in its course from the points which are apparent. We
see them mentally. Correct reasoning is the ideal assemblage of objects
in their actual order of co-existence and succession. It is seeing with
the mind's eye. False reasoning is owing to some misplacement of the
order of objects, or to the omission of some links in the chain, or to
the introduction of objects not properly belonging to the series. It is
distorted or defective vision. The terrified traveller sees a
highwayman in what is really a sign-post in the twilight; and in the
twilight of knowledge, the terrified philosopher sees a Pestilence
foreshadowed by an eclipse.

Let attention also be called to one great source of error, which is
also a great source of power, namely, that much of our thinking is
carried on by signs instead of images. We use words as signs of
objects; these suffice to carry on the train of inference, when very
few images of the objects are called up. Let any one attend to his