114 Cognition and Learning
resembles the Form of the Dog. Moreover, Plato posited the
existence of higher-level forms such as the Form of Beauty or
the Form of the Good. Thus, not only is a cat a cat because
it resembles the Form of the Cat, but a sculpture or painting
is objectively beautiful because it resembles the Form of
Beauty, and an action is objectively moral because it resem-
bles the Form of the Good. For Plato, if I say that justice is the
rule of the strong, I am in error, for tyranny does not resem-
ble the Form of the Good. We act unjustly only to the extent
our knowledge of the Good is imperfect.
Premodern relativism and skepticism were not inconsis-
tent with cognitive realism, because they rested on distrust
of human thought, not sensation or perception. One might
believe in the world of the Forms but despair of our ability to
know them, at least while embodied in physical bodies. This
was the message of Neoplatonism and the Christian thought
it influenced. Sophists liked to argue both sides of an issue to
show that human reason could not grasp enduring truth, but
they did not distrust their senses. Likewise, the skeptics were
wary of the human tendency to jump to conclusions and
taught that to be happy one should not commit oneself whole-
heartedly to any belief, but they did not doubt the truth of
individual sensations.
The Scientific Revolution and a New Understanding
of Cognition
The Scientific Revolution marked a sharp, almost absolute,
break in theories of cognition. It presented a new conception
of the world: the world as a machine (Henry, 1997). Platonic
metaphysical realism died. There were no external, transcen-
dental standards by which to judge what was beautiful or just,
or even what was a dog and what was a cat. The only reality
was the material reality of particular things, and as a result
the key cognitive relationship became the relationship be-
tween a perceiver and the objects in the material world he
perceives and classifies, not the relationship between the ob-
ject perceived and the Form it resembles. Aristotle’s percep-
tual realism died, too, as scientists and philosophers imposed
a veil of ideas between the perceiver and the world perceived.
This veil of ideas was consciousness, and it created psychol-
ogy as a discipline as well as a new set of problems in the
philosophy and psychology of cognition.
The Way of Ideas: Rejecting Realism
Beginning with Galileo Galilei (1564–1642), scientists dis-
tinguished between primaryandsecondarysense properties
(the terms are John Locke’s). Primary sense properties are
those that actually belong to the physical world-machine;
they are objective. Secondary properties are those added to
experience by our sensory apparatus; they are subjective.
Galileo wrote in his book The Assayer:Whenever I conceive any material or corporeal substance I
immediately... think of it as bounded, and as having this or
that shape; as being large or small [and] as being in motion or at
rest....From these conditions I cannot separate such a substance
by any stretch of my imagination. But that it must be white or
red, bitter or sweet, noisy or silent, and of sweet or foul odor,
my mind does not feel compelled to bring in as necessary ac-
companiments.... Hence, I think that tastes, odors, colors, and
so on... reside only in the consciousness [so that] if the living
creature were removed all these qualities would be wiped away
and annihilated.The key word in this passage is consciousness.For ancient
philosophers, there was only one world, the real physical
world with which we are in direct touch, though the Platon-
ists added the transcendental world of the Forms, but it, too,
was external to us. But the concept of secondary sense prop-
erties created a New World, the inner world of consciousness,
populated by mental objects—ideas—possessing sensory
properties not found in objects themselves. In this new repre-
sentational view of cognition—the Way of Ideas—we per-
ceive objects not directly but indirectly via representations—
ideas—found in consciousness. Some secondary properties
correspond to physical features objects actually possess. For
example, color corresponds to different wavelengths of light
to which retinal receptors respond. That color is not a primary
property, however, is demonstrated by the existence of color-
blind individuals, whose color perception is limited or ab-
sent. Objects are not colored, only ideas are colored. Other
secondary properties, such as being beautiful or good, are
even more troublesome, because they seem to correspond to
no physical facts but appear to reside only in consciousness.
Our modern opinion that beauty and goodness are subjective
judgments informed by cultural norms is one consequence of
the transformation of experience wrought by the Scientific
Revolution.Cartesian Dualism and the Veil of IdeasFor psychology, the most important modern thinker was
René Descartes (1596–1650), who created an influential
framework for thinking about cognition that was funda-
mental to the history of psychology for the next 350 years.
Descartes’ dualism of body and soul is well known, but it also
included the new scientific distinction of physical and mental
worlds. Descartes assumed living bodies were complex ma-
chines no different from the world-machine. Animals lacked