John Locke is really a very clear
and sensible writer, as you would soon see yourself if you had
the time to go look at his Essay Concerning Human Understanding
or any other of his philosophical writings. But the Essay
is also very lengthy, so I've not assigned you to read any
of it this quarter. Instead, I'm going to just tell you a few
of the main points he makes in that book. So after some introductory
words, the following mini-lecture will be divided into eight
of the key points Locke would most like you to learn from his
In his youth Locke seriously intended
to enter the seminary to become a priest, but in the end he chose
to study medicine instead. He became a physician, but practiced
only a little, devoting most of his time to writing and official
Locke considers epistemology to
be "first philosophy," because he considers it to be
the discipline that examines the instrument that does the knowing
and philosophizing, viz., the human mind. When you take a biology
course, your first lab will be to study and understand the microscope,
because the microscope is such a crucial instrument in learning
about biology. In a similar way, philosophy's first task should
be to examine how the human mind knows anything, which is the
task of epistemology. And the first task of epistemology should
be to find out if the mind is even capable of knowing anything,
and if it is, what are the limits to what it can know.
In his epistemological studies,
as we will see below, Locke relies much more heavily on direct
sensory experience than on logic and reason. He believes direct
experience to be a more reliable source of knowledge than logic
and reason. Descartes, a philosopher in the rationalist tradition,
chose to rely more on reason and logic for his analyses, but
Locke is, after all, a physician. Physicians rely on evidence
they get from their patients, they form hypotheses as to what
might be the underlying problem with their patient, and they
attempt treatments. If the treatments don't work they form another
hypothesis and attempt another treatment, and so on. Absolute
certitude may be something mathematicians can hope for, but the
physician must rely on experience and testing. Locke believes
that is also how we derive our knowledge about the world.
In any case, following are some of the key points
to learn from Locke's Essay.
I. There are no
Locke spends the entirety of Book
I in his Essay arguing that human beings have no inborn,
or innate, ideas in their minds at birth. Some of the rationalist
philosophers wanted to claim that when a human mind comes into
the world it already understands such fundamental principles
as the principle of non-contradiction - that a thing cannot both
be and not be at the same time in the same respect - and the
principle that the whole is more than the part. Locke does not
believe that we are born with any of these inborn ideas.
Locke believes that when a human
mind is first born - whether the birth of that human mind be
dated at the moment of parturition (birth), or earlier at the
moment of conception, or at some point in between - when the
human mind first comes into existence it does not come with any
inborn ideas. When it first exists it is a blank slate, a "tabula
rasa," an empty surface on which experience will then subsequently
write all that we ever know. We may be born with automatic instinctual
behaviors - such as automatic reflex motions in response to some
stimulus - but these are not ideas or perceptions or what today
we might call "contents of consciousness."
II. All ideas
come from experience
All contents of consciousness,
that is, everything that ever gets into the mind, comes into
it from one source only, and that source is experience. Experience
is the one source of input into the human mind.
There are two kinds of experience,
a. Experience of the outer world,
which he terms sensation, and from this mode of experience
we derive such notions as blue, round, solid, smooth, heavy,
b. Experience of the inner world,
which Locke terms reflection, and from this mode we get such
notions as fear, love, willing, doubting, affirming, thinking,
feeling, believing, remembering, planning, anticipating, and
For Locke, the term "idea"
is rather a technical term. By "idea" he means
anything that exists in consciousness, i.e., anything that exists
in the mind.
So to sum up these first two points,
no ideas are inborn in the mind; instead, all ideas, that is,
all contents of the mind, come to us ultimately from only one
source, experience (either sensation or reflection).
III. Simple and
There are basically two sorts of
ideas, simple and complex. Simple ideas include all our simple
sensory sensations such as red, cold, sweet, loud, soft, round,
Complex ideas are complexes of
simple ideas. For example, my sensory experience of a red ball
would include a mixture of the simple ideas of red, round, hard,
cool, etc. That complex of simple sensations goes into making
up my experience of the ball. That is to say, the sensation of
this red ball that is in my mind right now, i.e., the "idea"
of the ball, derives from the sensory experience of the ball
that I am presently experiencing.
In all his thinking about how knowing
works, Locke sees himself as following a very common sense way
of thinking. He does not see himself as saying anything particularly
abstruse or unusual, and certainly not as saying anything that
every common sense person wouldn't agree with. In this next section,
though, at least toward the end of it, based on common sense
though it is, we might at first think he is saying something
that common sense should not accept. But you might want to reserve
your judgment on that for a while.
IV. Ideas are
caused in us by qualities
(or sensations) in minds are caused by qualities in things.
For example, the sensation (or idea) of red in my mind is caused
by the quality of red in the thing.
So we now need a definition of
what a quality is. Here it is: A quality is a power in
a thing to cause an idea in a mind. So a quality is not a thing,
really, but is a power in a thing to cause an idea in
Now this is where it gets interesting.
There are two kinds of qualities, according to Locke, primary
and secondary. (He actually says there are three kinds of qualities,
but we're going to ignore the third kind for now.)
Primary qualities are those that
every physical object, every body, must have. Primary qualities
are actually in the physical object. There are only six
Every physical object, in order
to even be a physical object, must (according to Locke) have
solidity, must have some shape and size, must be either in motion
or at rest, must be either one or many, and must have some texture.
Secondary qualities, on the other
hand, are nothing but powers in things to produce a sensation
in a mind. Now this is an idea that we will need to explore in
a bit more detail.
Let's consider the old philosophical
question: When a tree falls in the forest and there is no one
around to hear it (i.e., no ears of any sort, no squirrels, reindeer,
frogs, lemurs or pachyderms), does it make a sound?
Locke's answer would be this. A
sound is a sensation in a mind. So "sound" is the kind
of existent that exists inside minds, not out in forests. Now
the sensation of sound in a mind is caused by a quality
out in the world, so let's examine what quality is out there
in the world that would cause that sound sensation in your mind.
When a tree falls, it is passing
through a medium (air), and in the process of passing through
that medium, it causes impact waves in that medium. See the illustration
(note: No graphic artists
were harmed or mistreated in the production of this image, and
the illustration is definitely not drawn to scale.)
Here's what's happening: In the
act of falling, the tree passes through a medium (air), and in
the process sets up impact waves which move through that medium
(much like dropping a pebble in a pool of water causes waves
to ripple outward in the medium of water). The impact waves are
not themselves sound, but if they strike an auditory apparatus
of some sort (like an eardrum-auditory nerve-brain combination)
then those waves can cause the sensation of sound ("Boom
and Crash") in those brains. So the sound is clearly inside
the brain, and what is outside in the world is a quality
that has the power to cause a sensation of sound in a
So if there are no brains or hearing
apparatuses around, then there are no sounds. In fact, if a tree
falls in the forest and there are people there, there
is still no sound in the forest. The sound is always in
the sensorium of the experiencing brain, not out there in the
world. What is out there in the world are impact waves
in a medium. Those waves are not themselves sound, but they can
cause sound if they impact a hearing apparatus (like the ones
for squirrels, lemurs, pachyderms humans, and others).
So sound is never "out there,"
no matter what sound we're talking about. It is always in a mind.
What is out there is some sort of quality which has the
power to cause a sensation in a mind.
What Locke would have us notice
here is how completely different the impact waves out there in
the world are from the sound sensation that exists in a mind.
These two realities are totally different kinds of entities.
Impact waves are out there moving through air. Sound is a sensation
that happens in a mind. Very different kinds of realities.
The concept of the transducer might
help us here. Locke did not have transducers around when he was
writing, but if he had, he would have loved the idea. A transducer
is something in the world of electronics. A transducer is basically
any electrical device that changes, or transduces, one form of
energy into another form of energy.
A lightbulb, for example, is a
transducer. It changes simple electricity (which is not visible)
into visible light. It is important to notice here that what
goes into the lightbulb (electricity) is not at all the same
thing that comes out of it (light). A very naïve person
who saw an electric cord leading into the lightbulb might wrongly
guess that the cord carried light into the lightbulb. That would
be naïve and wrong, of course. In much the same way, what
is impacting onto our hearing apparatus is a series of moving
waves in a medium. The impact of those waves on our eardrum,
and then on into the inner ear, the auditory nerve, and so on,
then transduces all that input into a sound. And what
Locke would have us notice is that a sound sensation is a very
different kind of animal than an impact wave in a medium.
A radio receiver is another example
of a transducer. It takes radio-frequency (RF) waves passing
through space and transduces them into something we can hear.
The RF waves are not themselves hearable until they have been
transduced by the receiver.
Our visual apparatus is also a
kind of transducer. Light waves come streaming into our eye and
impact on the surface of the retina. From that point on our visual
apparatus (retina, rods & cones, optical nerve, brain, etc)
transduces those light waves into a sensory experience with color,
shape, size, etc.
Now we sometimes assume that when
any two of us look toward the same object, we must each also
be having the same sensory experience. That is, we assume that
we each transduce those light waves into the same visual experience.
We might even assume that if my dog and I look toward the same
object that we will both see the same thing. Or that a lizard
and I would see the same thing. But the fact is that different
organisms, i.e., different visual apparatuses, in fact transduce
things quite differently than humans do.
Many years ago I saw a nice layout
in a magazine (unfortunately this was so many years ago - I think
I was still in college - that I no longer recall the magazine
or date) which showed an array of photographs taken of a single
daisy. The interesting thing was that each photograph was taken
through the visual apparatus of a different animal. I believe
the photographer may have been Lennart Nilsson, or at least was
a photographer who used lasers in his photography, and the photographer
was able to somehow get the camera to "see" the daisy
through the visual apparatus of several different animals. There
was a photo of the daisy as seen through the eye of a dog, a
lizard, a housefly, and so on. What was interesting was how astonishingly
different the daisy appeared through the visual apparatus of
those different organisms. In some it was colored certain ways,
in others it was colored other ways, in some it was shades of
gray with no other colors, in some the shape appeared nothing
like a daisy, in some the image was multiplied, and so on. In
some cases it appeared so different as to not even be recognizable
as a daisy.
It was actually a two-page layout,
with these dozen or so images laid out on the left side of the
display. Then on the right side of the display was a full page
photo of the daisy as seen through the human visual apparatus.
The implication of the layout seemed to be, since the photo of
the daisy as seen by a human was so much larger, that "This
is the way the daisy truly appears, viz., the way it is
seen by humans." But of course that implication would not
be accurate. The photo of the daisy as seen through the human
eyes should have been no larger than the photos through the eyes
of all the other organisms.
In any case, that photo layout
really brought home to me that we all transduce the stimuli that
come into us so that it will register in our brain in categories
that our brain is designed to understand. And that every other
organism does the same thing.
Now let's bring this back to John
Locke and his notion of secondary qualities. This notion that
our brains transduce the stimuli that come into them is exactly
what Locke meant when he said that secondary qualities are nothing
but powers in a thing to produce sensations in a mind.
So Locke's notion is that everything
we perceive besides the six primary qualities (solidity, size,
shape, texture, number, and motion/rest) are all secondary qualities.
They aren't really out there in the world in the way we think
they are. Sound isn't really out there in the world in the way
we think it is. Nor is color. Nor is temperature, taste, smell,
and so on. Neither are other sensations, like pain, for example.
We all realize that the pain we experience is not actually out
there in the world. We realize that pain is a sensation we have
in our brain/mind and that it is caused by something out there
in the world (a needle, a burn, etc) which is not itself pain.
It is just the cause of pain. We know the same thing about the
sensation of tickle, that it is not out there in the world. There
may be a feather out there in the world that some cruel person
is maliciously applying to us, but we realize that the tickle
is purely a sensation that exists in our mind (or brain). Well,
Locke just wants us to realize that all our other sensations
(except the six primary qualities) are also just in our minds.
V. Judgment constantly
alters our perception
This fifth point is simply that
there is a crucial difference between "sensation" and
"perception" (to put this in contemporary terms). Sensation
is simply the raw data that your senses bring into your brain,
and perception includes the judgments and interpretations that
you add to the sensations so that it ends up having some meaning
Perhaps an example will make this
I once went with a friend to the
Chicago Art Institute and on the second floor was an enormous
painting which took up one entire wall. It reached clear up to
the ceiling and all the way down to the floor. It was an amazingly
realistic and full-size painting of a hallway in an art museum,
so as you stood looking at it, you had the impression you were
looking down a hallway which then opened into another room of
the art gallery. You could see some paintings hanging on the
wall in the hallway, and one or two people standing looking at
them. It was all very realistic, and since it took up an entire
wall, with no noticeable frame around it, you could easily believe
that you were looking at an actual hallway.
Well, the Art Institute had to
put a big piece of plexiglas up in front of this painting because
people kept walking into it and bumping it.
The people who walked into the
painting were having certain raw sensations when they saw the
large painting (simple two-dimensional shapes of various sizes,
etc on a flat wall), and to those raw two-dimensional sensations
they added certain non-conscious judgments and interpretations
about what those shapes and sizes meant. They thus interpreted
the two-dimensional shapes to have three-dimensional meanings.
They interpreted the lines and colors they saw on the wall to
mean that there was open space in front of them.
According to Locke (and to most
contemporary sensory psychology too), we do this all the time
in all our perceptions. We receive only the raw sensation, but
we always overlay that raw sensation with our non-conscious judgments
and interpretations, and then what result from that are our perceptions.
So the formula would look like this:
sensation + judgment = perception
Or raw sensation, plus how we construe
those sensations, yields what our minds then perceive.
VI. Naive realism
vs critical realism
Locke's next point is the distinction
between naïve realism and critical realism.
First, though, we must distinguish
between the philosophy of realism and the philosophy of idealism.
Realism is any philosophy which holds that there is a real world
out there, and that our sensations and perceptions result from
an encounter with that real world. Idealism (as you would seen
in George Berkeley if you read him) is any philosophy which holds
that there is no real world out there, and that the only things
that exist are our perceptions and sensations.
Locke is definitely a realist.
He believes that there is a real world out there, and he believes
that's what good common sense teaches us too. But Locke wants
to distinguish between a naïve realism and a critical realism.
Naïve realism would be the unreflective belief that there
is a real world out there, and that our perceptions are an exact
copy, an exact replica, of what is actually out there in the
world. Naïve realism thinks of our senses as more or less
like a simple brownie camera, in which we open our senses to
the world and the world comes simply streaming into our mind
and leaves a perfect copy of itself in our perceptions. Naïve
realism would not be aware of how much our senses and brain transduce
the information that comes into them.
Locke considers himself to be a
critical realist. Critical realism is the belief that yes, there
is a real world out there, but our sensations and perceptions
are not simple copies of that real world. Critical realism believes
that our senses really do transduce and modify the incoming data
so that it will register in our minds in ways that make sense
to our brains and minds.
Perhaps a metaphor can help this more understandable.
Suppose a classroom full of little
laptop binary computers all sitting in a circle and having a
discussion amongst themselves. All any of them can perceive,
of course, are ones and zeros, since they are all binary computers
and that is all that binary computers can perceive. (If we want
to communicate with our computers, you know that we must translate
everything we want to say to them into ones and zeros; so if
I want to say "L" to my computer, I have to translate
that L into 10001010 so that the computer can understand it,
because strings of ones and zeros are all that its little processor
In any case, imagine all these
little computers thinking about what the real world out there
must actually be like. The naïve realists among them would
believe that the world consists of nothing but ones and zeros,
because that is exactly what they all see. The critical realists
among them would believe that yes, there must be a real world
out there, but it probably does not consist of only ones and
zeros. "The world comes streaming into us through our input
devices," says one critical realist computer," but
our input devices transduce the world into the categories that
we can understand, which is ones and zeros. The world out there
is not actually ones and zeros, but ones and zeros are the only
categories we have for perceiving the world, so if we're going
to see anything at all, it will have to register with us in those
Locke believes that we are just
like the binary computers, except that we have a few more categories
of perception than they do. (Later we will see that Immanuel
Kant believes that we have twelve or fourteen categories of perception.)
To sum up, naive realism believes
there is an isomorphic relationship between what we perceive
and what is actually out there in the world. You don't have to
learn much sensory psychology, though, before you discover that
Locke's critical realism is probably a lot closer to the mark
VII. Four kinds
Locke believes that there are only
four kinds of realities (existents) that exist in the world.
1. He believes there are selves
(or minds). He believes that we know about the existence of minds
both our own and those of other people -- by a process
he terms "intuiting."
2. The second kind of existent
Locke calls ideas, i.e., the contents of minds. He believes
we know about the existence of ideas by reflection.
3. The third kind of existent is things, or physical objects.
Locke believes that we know about the existence of things through
4. Fourthly, Locke believes that there is a God, and that
we know about God's existence by logical proofs for his existence.
(We will not be looking at any of the classical arguments for
the existence of God, but if you ever take a Philosophy of Religion
course you will learn about them there.)
VIII. Two big
Finally, there are two key questions
Locke considers it important to ask, and it may even be that
the asking of these two questions is more important than the
specific answers Locke gives to them.
The first question is this: Can we know that things continue
to exist during the intervals that they are not being observed
by anyone? For example, imagine that you are perceiving the mug
on your desk, but that you then turn away from it so that you
are no longer perceiving it in any way (and neither is anyone
else). You do not see it, feel it, hear it, smell it, or perceive
it in any way (and neither does anyone else). Then you turn back
and perceive it again. Then you turn away and are no longer perceiving
it. The question is this: during the intervals that the mug is
not being perceived, can we know that it continues to exist during
This may seem like a silly question,
but when one is doing epistemology it is important to examine
closely the assumptions that are made about what it is possible
to know. And Locke is willing to examine this assumption we all
seem to have, that things somehow continue in existence even
though no one is perceiving them. So that's question number one.
The second question is this: Even during the times that we are
directly observing an object can we know for sure that the object
Now the answers that Locke himself
proposed for these questions are not nearly as important as the
fact that he posed the questions. The next two philosophers who
follow Locke in the empiricist tradition - George Berkeley and
David Hume - take these two questions very seriously and suggest
answers very different from those that Locke offered.
Just for the record, though it
is not particularly important for our purposes here, here are
the answers that Locke proposed for these two questions.
Can we know that objects continue to exist even when they are
not being perceived by anyone? Answer: Well, perhaps we cannot
be absolutely certain of their continued existence during the
times when they are not being perceived, but common sense tells
us that in all probability they do continue to exist even
when not being perceived.
And can we know that objects exist even when they are being perceived?
Locke's answer: Surely no one would be so skeptical as to hold
that we cannot know objects exist when they are being directly
perceived. Common sense tells us that of course we can know that
objects exist during the intervals that we are directly perceiving
You might now ask yourself whether
you think Locke's answers to these two questions should be considered
adequate or not.
Berkeley, while he greatly
admired Locke and his work, did not consider that Locke had carried
his epistemological examinations quite far enough. I sometimes
wonder if Berkeley may have thought that Locke lost a bit of
his question-asking courage here when he caved in to too-simple
answers to these two questions.
So one of the big questions Berkeley
takes up when he writes both his Principles
of Human Knowledge and his Three
Dialogues Between Hylas and Philonous is the even more
central question: What does "to exist" actually mean?
We may assume that we understand this simple word which we use
so easily and frequently, but what exactly are we claiming when
we claim that a thing "exists?"
Berkeley's answer to this question is
a most interesting one.