osophy. Far more radical than the
earlier conception, it denied to animals not only the power of abstract
thought, but every form of psychic life whatever, and reduced the lower
form to a machine, which automatically reacted upon external stimuli.
This daring view, however, prevailed for only a comparatively short
period; but owing to the opposition which it aroused, it gave a
tremendous impetus to the study of animal consciousness. Most of the
great philosophers following Descartes, such as Locke, Leibniz, Kant,
and Schopenhauer, however greatly they may have differed in other
points, in this one returned to the Aristotelian point of view.

A third belief avers that animal and human consciousness do not differ
in essentials, but only in degree. This conclusion is regularly arrived
at by those who regard so-called abstract thought itself, as simply a
play of individual sensations and sensation-images, as did the French
and British associationists (Condillac and the Mills). The superiority
of man accordingly consisted in his ability to form more intricate
ideational complexes. Again, this conception of the essential similarity
of the human and the animal psyche has also always been arrived at by
the materialists (from Epicurus to C. Vogt and Buechner) who impute
reason to the animal form as well as to man. The same position is,
furthermore, taken by the evolutionists, including those who do not
subscribe to the doctrines of materialism. It has almost become dogma
with them that there exists an unbroken chain of psychic life from the
lowest protozoa to man. Haeckel, preeminently, though not always
convincingly, sought to establish such a graded series and thus to
bridge the chasm between the human and the animal consciousness.

Two tendencies, therefore, are discernible in animal psychology. The
one seeks to remove the animal psyche farther away from the human, the
other tries to bring the two closer together. It is undoubtedly true
that many acts of the lower forms reveal nothing of the nature of
conceptual thinking. But that others might thus be interpreted cannot be
denied. But need they be thus interpreted?--There lies the dispute. A
single incontrovertible fact which would fulfil this demand, [i.e.,
proof of conceptual thinking], would, at a stroke, decide the question
in favor of those who ascribe the power of thought to the lower forms.

At last the thing so long sought for, was apparently found: A horse that
cou