Inference is only a higher form of the same process.  We look from the window, see the dripping leaves and the wet ground, and infer that rain has fallen.  It is on inferences of this kind that all knowledge depends.  The extension of the known to the unknown, of the apparent to the unapparent, gives us Science.  Except in the grandeur of its sweep, the mind pursues the same course in the interpretation of geological facts as in the interpretation of the ordinary incidents of daily experience.  To read the pages of the great Stone Book, and to perceive from the wet streets that rain has recently fallen, are forms of the same intellectual process.  In the one case the inference traverses immeasurable spaces of time, connecting the apparent facts with causes (unapparent facts) similar to those which have been associated in experience with such results; in the other case the inference connects wet streets and swollen gutters with causes which have been associated in experience with such results.  Let the inference span with its mighty arch a myriad of years, or link together the events of a few minutes, in each case the arch rises from the ground of familiar facts, and reaches an antecedent which is known to be a cause capable of producing them.

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.