When I speak or think of any object as white, I and others perfectly understand what is meant, and a representation of this quality is instantly formed in our minds, in the generic type which was gradually constituted by primitive man by the combination of numerous special sensations, obvious to the sight, and subsequently expressed in speech.

In order that the word which corresponds to the quality may have a given sense, it is necessary to perceive the form of the concrete sensation which gave rise to it; for although the representation is indefinite or generic, that is, not obvious to the external senses, yet it is not physiologically distinct from the sensation of the quality described; the perception of that quality is present by the aid of memory to the inner consciousness.

It is therefore evident that the physiological elements of consciousness are actually contained in so-called abstract ideas, although it is sometimes asserted that they are purely spiritual and intellectual acts, remote from every physiological process of fact and sense.  An actual physiological fact (colour in this instance) corresponds to the idea in the nervous centres, and reproduces the sensation due to the perception of special objects, whose physical quality of whiteness we have perceived, and this sensation makes part of the abstract, or rather indefinite conception.

In fact, all which is not actually present to the mind—­and the present is an infinitesimal fraction of knowledge—­is reproduced by the memory, and this is effected by the molecular movements of the human brain, and by what may be called the ethereal modifications which took place when the sensations, perceptions, and acts first occurred.  If the cells vibrate, and the organs of the brain are affected by the recollection of past ideas and acts, just as when they actually occurred (and this appears from Schiff’s experiences as to the increase of the brain in heat and volume during dreams), this vibration will be still more marked when any quality which affects our senses is reproduced in the mind.

The particular form of the quality as it appears in a definite object is certainly wanting in the abstract conception; it remains in the first stage of pure sensation, like a spontaneous act of observation, and it is transformed into apprehension by the mental faculty.  But the inward consciousness of the quality is actual, psychical, and physical.  The abstract conception is a psychical symbol composed of idea and consciousness, or rather of act and consciousness; both are fused into a logical conception of indefinite form, yet consisting of real elements, that is, of cerebral motions and of sensations.