It has been an issue of controversy whether or not any animals under man have the ability to rise above the
perceptual level and form even primitive concepts. Mortimer J. Adler, in his scholarly work The Difference of Man
and the Difference It Makes, presents a comprehensive review and analysis of the evidence and arguments on both
sides of the controversy, and argues persuasively for the negative view. In my judgment, he has provided an
unanswerable case to support the conclusion that there are no valid grounds for attributing concepts to any animal
other than man, that man is truly unique among living species in being the conceptualizing animal.^1
It is extremely doubtful if the lowest forms of conscious organisms are capable even of perceptions. The likeliest
hypothesis is that they are capable of receiving and reacting only to disparate, unretained, and unintegrated
sensations.
The higher forms of conscious life, under man, exhibit the ability of forming not only separate, unconnected
percepts, but, in addition, "perceptual residues" and "perceptual abstractions." Perceptual residues (or perceptual
traces) are "memory-images that function representatively, i.e., in place of sensory stimuli that are no longer
themselves operative."^2 Perceptual abstraction refers to the process whereby the animal is able to recognize
similarities and differences among sensible particulars, to recognize that a number of sensible particulars are of the
same kind and are different from other sensible particulars. This ability accounts for the highest expressions of
"intelligence" that animals under man exhibit; but this ability does not, as such, require or imply the capacity to
form concepts, which consists not merely of recognizing that a number of sensible particulars are of the same kind,
but of identifying explicitly of what the kind consists.
In his illuminating analysis of the idea of perceptual abstractions, Adler writes:
For example, when an animal has acquired the disposition to discriminate between triangles and circles—in spite of differences in
their size, shape, color or position, and whether or not they are constituted by continuous lines or dots —that acquired disposition
in the animal is the perceptual attainment I have called a perceptual abstraction. This disposition is only operative in the presence
of an appropriate sensory stimulus, and never in its absence, i.e., the animal does not exercise its acquired disposition to
recognize