- NAIVE REALISM OR OBJECTIVISM.
This is simplest theory of perception. In addition to the
assumptions common to all forms of empiricism, naive realism
makes the following further assumptions concerning the knowing
of objective reality:
- We perceive objective reality (physical objects) directly.
- These objects exist independently of ourselves.
- The characteristics of these objects are as we perceive them.
The problem with naive realism is that our perceptions of the object
can and do vary, whereas the object (naive realism assume) do not.
- COMMON SENSE REALISM.
Common sense realism is that form of naive realism tending
toward dualistic realism. This was the theory of knowledge of a school of
Scotish thinkers founded by Thomas Reid (1710-1796) which attempted to
set up a theory of knowledge which whould support the realistic belief of the
man on the street. This theory held that we perceive the external world
directly and that the sense-data either do not exist or play subordinate role
in perception. In Aristotle's psychology common sense is the faculty by which
the common sensibles are perceived. Aristotle probably attributed to this
faculty the functions of perceiving what we perceive and of uniting the data
from the different senses into a single object. In his An Inquiry into the
Human Mind on the Principle of Common Sense (1795), Reid took this concept
to emphasize that the common consciousness of man is basic. He held that
all humans possess, by nature, a common set of capacities - both
epistemological and ethical - through which they could grasp the basic
realities of nature and morality. He opposed the theory of ideas of Berkeley
and Hume that the perception of ideas are our sole source of knowledge of the
world.
This theory is due to the influence of John Locke on Modern Western thought.
When some philosophers, following John Locke, made sense-knowledge
more complicated by interposing "ideas" between our minds and the real world,
so that these ideas, they said, were the immediate objects in our minds,
and hence we do not have immediate direct knowledge of the objects,
but only of the ideas in our minds, David Hume raised the question of
how do we know that these ideas correspond with what is actually there.
The answer of Thomas Reed was akin to Samuel Johnson's kicking a rock
to refute the similar theory proposed by Bishop Berkeley.
Reed answered that only philosophers would take seriously this
skeptical doctrine with its absurd implications. Everyone in his senses
believes such truths as the existence of the real world, cause and effect,
and the continuity of the self; they believe that the mind has the ability
to know such things. If philosophers question such truths, so much the worst
for the philosophers. The common-sense of mankind, whether of the man behind
the plow or the man behind the desk, is the surest guide to the truth.
- EPISTEMIC DUALISTIC REALISM.
This theory of perception was developed by the English philosopher
John Locke (1632-1704) in his book
Essay Concerning Human Understanding
Epistemic dualistic realism or dualism makes the following
assumptions concerning the knowing of objective reality:
- Our perception of the object and the object itself are two
different things. Hence the dualism.
- Our perception of the object is caused by the object.
- Our perception of the object is like a copy, picture or
representation of the object, which is like its cause,
the object.
This theory denies assumptions one and three of naive realism.
- Instead of assumption one of naive realism, it maintains an
indirect knowledge of the object but a direct knowledge of
ideas or perceptions only.
- Instead of assumption three of naive realism, it maintains the
distinction between primary and secondary qualities. Primary
qualities are those qualities of the object that are in the
object, such as size, shape, hardness, etc. Secondary qualities
are those other qualities that are in the knowing subject.
Primary qualities have objective existence in the object, while
secondary qualities have subjective existence in the subject only.
- But dualism retains assumption number two of naive realism.
These objects have an existence independent of ourselves.
Hence this theory is called realism.
The problems with epistemic dualistic realism are the following:
- What assurance do we have that there is any correspondence
at all between our perceptions, "ideas," and their external
cause, the object?
- How do we know there is an external cause, an object? Do
our senses give us a perception of that cause?
- EPISTEMIC IDEALISM OR SUBJECTIVISM.
This theory of perception was developed by the English philosopher,
George Berkeley (1685-1753). Epistemic idealism makes the
following assumptions concerning the knowledge situation:
- Since the mind knows directly only ideas or perceptions and
not the objects, we cannot know of the existence of the objects
outside of our perceptions.
- All qualities are subjective, that is, relative to the perceiving
mind. Since things are a collection of ideas, things cannot exist
apart from a knowing mind or subject. Things do not have absolute
or independent existence in themselves. Hence no material
substances. The source of our ideas or perceptions are not physical.
- Objects do not have an existence independently of our perceptions
of them. The complex of sensations are the object. For a thing
to be, it must be perceived (Esse est percipi).
Conclusion: Epistemic Idealism reduces to Solipism. That is,
I and my ideas alone exist. This leads to the egocentric predicament.
How do I know whether there are any other minds besides my own?
Berkeley avoided this conclusion by the introduction of God. All
perceptions of objects and other minds are placed there by God.
- SKEPTICISM.
Skepticism is the ultimate and logical conclusion of empiricism.
The ancient version was developed by Protagoras and the modern
form by David Hume (1711-1766). Skepticism makes the following
assumptions concerning the knowledge situation:
- All we know are our sense impressions and the ideas built up
from them.
- These sense impressions are separate and distinct from one
another. Sense impressions gives us no necessary connection
between them.
Conclusion: There is no grounds to justify belief
- in the existence of enduring physical objects which cause the sense
impressions and which preserve their identity from one moment to
the next or
- in the enduring selves or minds which apprehend
the sense impressions or underlie the string of impression or
memories of them.
Why do we believe in their existence?
Hume's answer: habit and custom.
Need a better reason but empiricism cannot provide it.
Hence empiricism leads to skepticism. There is no human knowledge of
anything. Hence there is no truth; truth is unattainable.
But skepticism is self-contradictory. Skepticism
asserts that it knows that knowledge of anything is not possible.
- CRITICAL IDEALISM.
The skepticism of Hume struck the German philosopher Immanuel Kant
(1724-1804) as destroying the foundations of philosophy and science.
He tells us that Hume "interrupted my dogmatic slumber, gave my
investigations in the field of speculative philosophy a quite new
direction." He saw that, if Hume was right, there are no grounds
in experience for indispenable universal or general judgments, such
as inductive generalization and causal inference. The problem is,
says Kant, how are universal and necessary judgments possible, or,
in Kant's terminology, how are a priori synthetic judgments possible?
As Hume pointed out, sense experience gives us separate and unconnected
particulars, X then Y, X then Y, etc. Whence comes the universal and
necessary character of the judgments X causes Y ?
Kant's answer is that universal and necessary judgments are possible
because of the structure of mind itself. The mind is not an inert
block of wax, a tabula rasa, which passively receives and
records the impressions of the senses, as the British empiricists like
Locke held. The mind is creative, dynamic and active process; it is
equipped with certain innate forms which order and interpret sense
experience.
- The forms of the mind orient the data of sense experience in space
and time. Space and time have no objective existence independently
of us. They are forms of mind which are impressed on the sense data.
- After the sense data is oriented in space and time, the part of the
mind Kant called the "understanding" takes over. The understanding
possesses twelve innate categories with which the mind operates
on the sense experience to produce universal and necessary judgments.
This results in conceptual knowledge that is universal and necessay.
The senses provide immediately perceptual knowledge of particulars;
percepts come from experience and concepts are formed by the internal
structure of the mind. Both percepts and concepts are necessary
elements in any act of knowledge which does not lead to deception.
As Kant says, "Concepts without percepts are empty and percepts
without concepts are blind." Conceptual knowledge is subjective
and perceptual knowledge is objective, derived from the objects of
the senses.
Conclusion: The dramatic conclusion of Kant's theory of knowledge is
that we can never know the "real" nature of the external world or any
object in it, if by "external world" we mean the world independent
of human knowledge. What we do know are the appearances (phenomena)
produced by the operation of the space-time forms of the mind.
Things-in-themselves (noumena) are unknowable and forever hidden
from us. There is really no way we can know whether our concepts really
correspond to things-in-themselves. This is a just another form of
skepticism; Kant started out to overcome Hume's skepticism and ends
up with another form of skepticism. As it is often said Hume gave
Kant the problem of knowledge and Kant gave it back as if it were
its solution.