the corporate "I," which is quite abstract.

This abstract "I"-concept, that belongs only to the adult, thinking
human being, comes into existence in exactly the same way that other
concepts do, viz., by means of the individual ideas from which it
results, as e. g., the forest exists only when the trees exist. The
subordinate "I's," that preside over the separate sense-departments, are
in the little child not yet blended together, because in him the organic
connections are still lacking; which, being translated into the language
of psychology, means that he lacks the necessary power of abstraction.
The co-excitations of the sensory centers, that are as yet impressed
with too few memory-images, can not yet take place on occasion of a
single excitation, the cerebral connecting fibers being as yet too
scanty.

These co-excitations of parts of the brain functionally different, on
occasion of excitation of a part of the brain that has previously often
been excited together with those, form the physiological foundation of
the psychical phenomenon of the formation of concepts in general, and so
of the formation of the "I"-concept. For the special ideas of all
departments of sense have in all beings possessed of all the senses--or
of four senses, or of three--the common quality of coming into existence
only under conditions of time, space, and causality. This common
property presupposes similar processes in every separate sense-center of
the highest rank. Excitations of one of these centers easily effect
similar co-excitations of centers that have often been excited together
with them through objective impressions, and it is this similar
co-excitement extending itself over the cerebral centers of all the
nerves of sense that evokes the composite idea of the "I."

According to this view, therefore, the "I" can not exist as a unit, as
undivided, as uninterrupted; it exists only when the separate
departments of sense are active with their _egos_, out of which the "I"
is abstracted; e. g., it disappears in dreamless sleep. In the waking
condition it has continued existence only where the centro-sensory
excitations are most strongly in force; i. e., where the attention is on
the strain.

Still less, however, is the "I" an aggregate. For this presupposes the
exchangeability of the component parts. The seeing _ego_, however, can
just as little have its place made good by a substitute as can the
hearing one, the tasting one, etc.