Enlightenment began with an unparalleled confidence in human reason. The new
science's success in making clear the natural world through Locke, Berkeley, and
Hume affected the efforts of philosophy in two ways. The first is by locating
the basis of human knowledge in the human mind and its encounter with the
physical world. Second is by directing philosophy's attention to an analysis of
the mind that was capable of such cognitive success. John Locke set the tone for
enlightenment by affirming the foundational principle of empiricism: There is
nothing in the intellect that was not previously in the senses. Locke could not
accept the Cartesian rationalist belief in innate ideas. According to Locke, all
knowledge of the world must ultimately rest on man's sensory experience. The
mind arrives at sound conclusions through reflection after sensation. In other
words the mind combines and compounds sensory impressions or "ideas"
into more complex concepts building it's conceptual understanding. There was
skepticism in the empiricist position mainly from the rationalist orientation.
Locke recognized there was no guarantee that all human ideas of things genuinely
resembled the external objects they were suppose to represent. He also realized
he could not reduce all complex ideas, such as substance, to sensations. He did
know there were three factors in the process of human knowledge: the mind, the
physical object, and the perception or idea in the mind that represents that
object. Locke, however, attempted a partial solution to such problems. He did
this by making the distinction between primary and secondary qualities. Primary
qualities produce ideas that are simply consequences of the subject's perceptual
apparatus. With focusing on the Primary qualities it is thought that science can
gain reliable knowledge of the material world. Locke fought off skepticism with
the argument that in the end both types of qualities must be regarded as
experiences of the mind. Lockes Doctrine of Representation was therefore
undefendable. According to Berkley's analysis all human experience is
phenomenal, limited to appearances in the mind. One's perception of nature is
one's mental experience of nature, making all sense data "objects for the
mind" and not representations of material substances. In effect while Locke
had reduced all mental contents to an ultimate basis in sensation, Berkeley now
further reduced all sense data to mental contents. The distinction, by Locke,
between qualities that belong to the mind and qualities that belong to matter
could not be sustained. Berkeley sought to overcome the contemporary tendency
toward "atheistic Materialism" which he felt arose without just cause
with modern science. The empiricist correctly aims that all knowledge rests on
experience. In the end, however, Berkeley pointed out that experience is nothing
more than experience. All representations, mentally, of supposed substances,
materially, are as a final result ideas in the mind presuming that the existence
of a material world external to the mind as an unwarranted assumption. The idea
is that "to be" does not mean "to be a material substance;"
rather "to be" means "to be perceived by a mind." Through
this Berkeley held that the individual mind does not subjectively determine its
experience of the world. The reason that different individuals continually
percieve a similar world and that a reliable order inheres in that world is that
the world and its order depend on a mind that transcends individual minds and is
universal (God's mind). The universal mind produces sensory ideas in individual
minds according to certain regularities such as the "laws of nature."
Berkeley strived to preserve the empiricist orientation and solve Lockes
representation problems, while also preserving a spiritual foundation for human
experience. Just as Berkeley followed Locke, so did David Hume of Berkeley. Hume
drove the empiricist epistemological critique to its final extreme by using
Berkeley's insight only turning it in a direction more characteristic of the
modern mind. Being an empiricist who grounded all human knowledge in sense
experience, Hume agreed with Lockes general idea, and too with Berkeley's
criticism of Lockes theory of representation, but disagreed with Berkeley's
idealist solution. Behind Hume's analysis is this thought: Human experience was
indeed of the phenomenal only, of sense impressions, but there was no way to
ascertain what was beyond the sense impressions, spiritual or otherwise. To
start his analysis, Hume distinguished between sensory impressions and ideas.
Sensory impressions being the basis of any knowledge coming with a force of
liveliness and ideas being faint copies of those impressions. The question is
then asked, What causes the sensory impression? Hume answered None. If the mind
analyzes it's experience without preconception, it must recognize that in fact
all its supposed knowledge is based on a continuous chaotic volley of discrete
sensations, and that on these sensations the mind imposes an order of its own.
The mind can't really know what causes the sensations because it never
experiences "cause" as a sensation. What the mind does experience is
simple impressions, through an association of ideas the mind assumes a causal
relation that really has no basis in a sensory impression. Man can not assume to
know what exists beyond the impressions in his mind that his knowledge is based
on. Part of Hume's intention was to disprove the metaphysical claims of
philosophical rationalism and its deductive logic. According to Hume, two kinds
of propositions are possible. One view is based purely on sensation while the
other purely on intellect. Propositions based on sensation are always with
matters of concrete fact that can also be contingent. "It is raining
outside" is a proposition based on sensation because it is concrete in that
it is in fact raining out and contingent in the fact that it could be different
outside like sunny, but it is not. In contrast to that a proposition based on
intellect concerns relations between concepts that are always necessary like
"all squares have four equal sides." But the truths of pure reason are
necessary only because they exist in a self contained system with no mandatory
reference to the external world. Only logical definition makes them true by
making explicit what is implicit in their own terms, and these can claim no
necessary relation to the nature of things. So, the only truths of which pure
reason is capable are redundant. Truth cannot be asserted by reason alone for
the ultimate nature of things. For Hume, metaphysics was just an exalted form of
mythology, of no relevance to the real world. A more disturbing consequence of
Hume's analysis was its undermining of empirical science itself. The mind's
logical progress from many particulars to a universal certainty could never be
absolutely legitimated. Just because event B has always been seen to follow
event A in the past, that does not mean it will always do so in the future. Any
acceptance of that "law" is only an ingrained psychological
persuasion, not a logical certainty. The causal necessity that is apparent in
phenomena is the necessity only of conviction subjectively, of human imagination
controlled by its regular association of ideas. It has no objective basis. The
regularity of events can be perceived, however, there necessity can not. The
result is nothing more than a subjective feeling brought on by the experience of
apparent regularity. Science is possible, but of the phenomenal only, determined
by human psychology. With Hume, the festering empiricist stress on sense
perception was brought to its ultimate extreme, in which only the volley and
chaos of those perceptions exist, and any order imposed on those perceptions was
arbitrary, human, and without objective foundation. For Hume all human knowledge
had to be regarded as opinion and he held that ideas were faint copies of
sensory impressions instead of vice - versa. Not only was the human mind less
than perfect, it could never claim access to the world's order, which could not
be said to exist apart from the mind. Locke had retained a certain faith in the
capacity of the human mind to grasp, however imperfectly, the general outlines
of an external world by means of combining operations. With Berkeley, there had
been no necessary material basis for experience, though the mind had retained a
certain independent spiritual power derived from God's mind, and the world
experienced by the mind derived its order from the same source.