Summary, Book I: “Of the Understanding”
Hume begins by arguing for the validity of empiricism,
the premise that all of our knowledge is based on our experiences,
and using this method to examine several philosophical concepts.
First, he demonstrates that all of our complex ideas are formed
out of simpler ideas, which were themselves formed on the basis
of impressions we received through our senses. Therefore, ideas
are not fundamentally different from experiences. Second, Hume defines
“matters of fact” as matters that must be experienced, not reasoned
out or arrived at instinctually. Based on these two claims, Hume
attacks metaphysical systems used to prove the existence of God,
the soul, divine creation, and other such ideas. Since we have no
experience of any of these things and cannot receive a direct impression
of them, we have no real reason to believe that they are true.
Hume systematically applies the idea that ideas and facts
come from experience in order to analyze the concepts of space,
time, and mathematics. If we have no experience of a concept, such
as the size of the universe, that concept cannot be meaningful.
Hume insists that neither our ideas nor our impressions are infinitely
divisible. If we continued to try to break them down ad infinitum,
we would eventually arrive at a level too small for us to perceive
or grasp conceptually. Since we have no experience of infinite divisibility,
the idea that things or ideas are infinitely divisible is meaningless.
Mathematics, however, is a system of pure relations of ideas, and
so it retains its value even though we cannot directly experience
its phenomena. Many of its principles do not hold in matters of
fact, but it is the only realm of knowledge in which perfect certainty
is possible anyway.
Hume introduces two of his three tools of philosophical
inquiry, the “microscope” and the “razor.” The microscope is the
principle that to understand an idea we must first break it down
into the various simple ideas that make it up. If any of these simple
ideas is still difficult to understand, we must isolate it and reenact
the impression that gave rise to it. The razor is the principle
that if any term cannot be proven to arise from an idea that can
be broken into simpler ideas ready for analysis, then that term
has no meaning. Hume uses his razor principle to devalue abstract
concepts pertaining to religion and metaphysics.
Despite his apparent hostility to abstract ideas of a
metaphysical nature, Hume does not deem all abstract ideas worthless.
Hume argues that the mind naturally forms associations between ideas from
impressions that are similar in space and time. In the mind, a general
term becomes associated with further specific instances of those
similar impressions and comes to stand for all of them. This process
explains why we can visualize particular events that we may not
have actually experienced, based on their association with those events
that we have experienced.
Hume’s third philosophical tool is the “fork,” the principle
that truths can be divided into two kinds. The first kind of truth
deals with relations of ideas, such as true statements in mathematics—for example,
that the sum of the angles in a triangle equals 180 degrees. These
kinds of truth are necessary—once they’ve been proven, they stay
proven. The second kind of truth deals is in matters of fact, which
concerns things that exist in the world.
Analysis
The theories Hume develops in the Treatise have
their foundations in the writings of John Locke and George Berkeley,
and Hume is associated with these two men as the third in the series
of great British empiricists. Like Hume, Locke denied the existence
of innate ideas, dividing the sources of our ideas into two categories:
those derived from sensation through the use of our sense organs
and those derived from reflection through our own mental processes. Hume
makes use of Locke’s distinction in his own theory of ideas, though
he alters the terminology. For Hume, sensations and reflections
both fall under the term impressions, while he
reserves the term ideas for the results of mental
processes such as imagination and memory. Hume’s discussion of abstract
ideas rests on his acceptance of Berkeley’s claim that the idea
we have of a general term always springs from a specific experience,
though used in a general way. Hume praised this explanation but
further clarified how a general term could stand for several similar,
but specific, experiences.
