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IDER SYMPOSIUM 2010
The mind as a reality modeler
and limitations on our knowledge of reality
Marius Cohen
The Department of Philosophy and The Program of Cognitive Science
Ben Gurion University
In this lecture I will put forward the following claims:
1. There is a large gap between the way we perceive reality and reality itself.
2. This gap usually passes unnoticed because although we do not have direct access
to reality, our mind creates a fairly good model of it.
3. Some philosophers believe that we do have direct access to some aspects of reality
by mental representations which resemble those physical features of the external
world which they represent.
4. There are good reasons to believe that this is not so.
5. Therefore we cannot in principle have direct knowledge of reality itself and we are
trapped in the model our mind creates for us.
1. Appearance and Reality
The question of the relation between how we perceive reality and the nature of reality itself
- the question of appearance vs. reality - is a long standing one. Bertrand Russell, the 20th
century British philosopher, wrote1:
1Bertrand
Russell, Problems of Philosophy, § 1.
… let us concentrate attention on the table. To the eye it is oblong, brown and
shiny, to the touch it is smooth and cool and hard; when I tap it, it gives out a
wooden sound...; but as soon as we try to be more precise our troubles begin… if
several people are looking at the table at the same moment, no two of them will
see exactly the same distribution of colours, because no two can see it from
exactly the same point of view, and any change in the point of view makes some
change in the way the light is reflected… Here we have already the beginning of
one of the distinctions that cause most trouble in philosophy -- the distinction
between 'appearance' and 'reality', between what things seem to be and what
they are… there is no colour which preeminently appears to be the colour of the
table, or even of any one particular part of the table -- it appears to be of different
colours from different points of view…This colour is not something which is
inherent in the table, but something depending upon the table and the spectator
and the way the light falls on the table.
The same thing applies to the texture. With the naked eye… the table looks
smooth and even. If we looked at it through a microscope, we should see
roughnesses and hills and valleys, and all sorts of differences that are
imperceptible to the naked eye.
The shape of the table is no better. We are all in the habit of judging as to the
'real' shapes of things, and we do this so unreflectingly that we come to think we
actually see the real shapes. But, in fact, as we all have to learn if we try to draw,
a given thing looks different in shape from every different point of view. If our table
is 'really' rectangular, it will look, from almost all points of view, as if it had two
acute angles and two obtuse angles.… the 'real' shape is what interests us as
practical men. But the 'real' shape is not what we see; it is something inferred
from what we see.
Thus it becomes evident that the real table, if there is one, is not the same as
what we immediately experience by sight or touch or hearing. The real table, if
there is one, is not immediately known to us at all, but must be an inference from
what is immediately known. Hence, two very difficult questions at once arise;
namely, 1) Is there a real table at all? (2) If so, what sort of object can it be?
It is plain that if we are to know anything about the table, it must be by means of
the sense-data -- brown colour, oblong shape, smoothness, etc. -- which we
associate with the table; but, for the reasons which have been given, we cannot
say that the table is the sense-data, or even that the sense-data are directly
properties of the table. Thus a problem arises as to the relation of the sense-data
to the real table, supposing there is such a thing.
…if we take any common object of the sort that is supposed to be known by the
senses, what the senses immediately tell us is not the truth about the object as it
is apart from us, but only the truth about certain sense-data which, so far as we
can see, depend upon the relations between us and the object. Thus what we
directly see and feel is merely 'appearance', which we believe to be a sign of
some 'reality' behind. But if the reality is not what appears… have we any means
of finding out what it is like?
The one thing we know about it [the table] is that it is not what it seems. …
[science] tells us it is a vast collection of electric charges in violent motion.
In recent years there has been much controversy over the meaning of the term "sense
data" and whether its use is justifiable, but what concerns us here is the fact that the gap
between reality and how we perceive it is not only a matter of different perspectives or
different
conditions of perception, but also a matter of different categories: physical
features vs. mental states.
The world is accessible to us through our senses, and through them alone: We see, hear,
feel, smell and taste, thus forming our beliefs of the world and its nature. We have no
direct means to experience the world, we only have access to our mental states. To some
extent we are trapped in our mind, depending on our sensory input to learn about the
world and its nature. But how reliable are our senses? Do they really present to us the
world as it really is, or is the real world different from what our mind tells us? Well, modern
science tells us that there is a significant gap between the physical nature of the world and
how our consciousness perceives it: our sense of sight, for example, which informs us
about our environment more than any other sense, presents to us an illuminated and
colorful world. But light is nothing but tiny particles (photons) emitted from a light source,
bouncing from the bodies around us to our retinas, thus allowing us to see our
surroundings (after the data has been processed by the brain). In daytime the world seems
illuminated, but it is only so presented to us by our brains due to vast amounts of photons
that reach our eyes. The world itself, in contrary to how it is perceived, is to some extent
completely dark (I say 'to some extent', because darkness is a concept based on vision,
too, but it's probably the best available description for this property of the world). The
colorfulness of the world is a mere illusion, too: The world itself is colorless (including all
shades of white, black and gray, so the world does not even resemble a black-and-white
movie). The colors we see are the product of our mind: the experience of color is induced
by electromagnetic waves of certain frequencies reaching our eyes and causing sensory
stimulus, which is electrically and chemically transmitted to certain parts of our brain,
which then (mysteriously) produces that wonderful color experience.
Our inner world is also rich in sounds: speech, music, noises of all sorts. But the external
world, nature in itself, is totally silent! It is our brain which, following sensory information
induced by air vibrations, produces sounds for us (and maybe this understanding is the
origin of the question whether a tree falling in the forest when no one is around still makes
a sound). Sounds are in our mind only, they are not part of the physical reality.
We also perceive the world as rich in scents, but scents are only our mind's interpretations
of the different kinds of molecules stimulating the receptors in our noses. The world in itself
is devoid of scents.
Even the touching experience, which perhaps more than any other sense experience
makes the world feel concrete to us, is nothing but a mental state, and so are the
experiences of heat and cold and all other sense experiences that participate in our
perception of reality.
Therefore, the way the world is presented to us is very different than how it really is, and it
seems that we have no way of experiencing it directly but only via our senses. Immanuel
Kant, the great 18th century German philosopher, claimed that we cannot know anything
of "the thing in itself" (Ding an sich). Although it is the source of our sensory information,
the world revealed to us is not "the thing in itself", but only our perception of it. According
to Kant even space and time are the products of our consciousness, and do not belong to
"the thing in itself", which cannot be directly experienced.
2. The Mind as a Reality Modeler
If our perception of reality, as we have seen above, is so different than reality itself, how is
it that we manage to survive and thrive in the world? How is it that we manage to interact
so successfully with our surroundings, change it to our advantage and protect ourselves
from hazards? The answer is that our mental states, although different in kind than our
physical environment, make a good enough representation of it. Our mind creates a model
of the external world, and that model, albeit not perfect, is a good enough representation of
those features of reality our lives and actions depend on. The mental representation of an
approaching lion is very different from the real thing, but usually one does not occur
without the other, so we can act accordingly: run away, climb a tree or use a weapon,
depending on our mental representations of the available options (if one does occur
without the other, as may be the case if one is blind or hallucinating, survival is indeed at
stake).
So, there is a good correlation between the external world and its mental representation,
which makes a good model of it. Actually, our mind is so efficient as a reality modeler that it
makes it hard for us to even realize that our perception of the world is nothing but a lively
model of the real thing. We needed philosophical insights and science to tell us there is a
difference between those two and how big that difference is.
But can science not tell us also what reality is really like? We now know that colors are
mental representations of electromagnetic waves, sounds are our mind's interpretation of
air vibrations, scents are mental representations of certain chemicals and so forth.
Although our knowledge of reality is gained indirectly, does science not reveal all its
features to us? Hardly so. Careful examination of the matter, as we will next see, gives us
good reasons to believe that at least some features of "the thing in itself" are forever to
elude us, no matter how much science we come up with. We will see that we are doomed
to be forever trapped in the model of reality our mind creates for us.
3. Primary and Secondary qualities
John Locke, the great 17th century English philosopher, following a tradition which started
with Galileo, made clear the distinction between two kinds of qualities 2:
Qualities thus considered in bodies are of two kinds. First, there are those that are
utterly inseparable from the body, whatever state it is in. Qualities of this kind are
the ones that a body doesn’t lose, however much it alters, whatever force is used
on it, however finely it is divided. Take a grain of wheat, divide it into two parts,
each part has still solidity, extension, shape, and mobility; divide it again, and it
still retains those qualities; go on dividing it until the parts become imperceptible,
each part must still retain all those qualities. . . . I call them original or primary
qualities of body, which I think we may observe to produce simple ideas in us,
viz. solidity, extension, shape, motion or rest, and number.
Secondly, there are qualities that are, in the objects themselves, really nothing but
powers to produce various sensations in us by their primary qualities, i.e. by the
size, shape, texture, and motion of their imperceptible parts. Examples of these
are colours, sounds, tastes, and so on. I call these secondary qualities.
So, Locke follows the tradition of distinguishing between features of reality whose mental
representations presumably resemble them (primary qualities), such as solidity,
extension, shape, and mobility, and features of reality whose mental representations do
not resemble them (secondary qualities), such as colors, sounds, and tastes. If this
distinction is correct, then we can have a glimpse of reality: We perceive its primary
qualities as they are, and can get science to help us to figure out at least some of its
2
J. Locke, An Essay Concerning Human Understanding, 2.8.
secondary qualities, those that can be analyzed in terms of primary ones. Colors and
sounds for example are known to represent sorts of vibrations, and these can be
expressed in terms of (among other things) changes in space and time, of which at least
space is considered to be primary, and time may be viewed as such too.
4. The Problem of Comparison
However, not everybody agrees to the above distinction between primary and secondary
qualities. George Berkeley, the 17th and 18th century Anglo-Irish philosopher, wrote 3 :
Some philosophers distinguish ‘primary qualities’ from ‘secondary qualities’: they
use the former term to stand for extension, shape, motion, rest, solidity and
number; by the latter term they denote all other perceptible qualities, such as
colours, sounds, tastes, and so on. Our ideas of secondary qualities don’t
resemble anything existing outside the mind or unperceived, they admit; but they
insist that our ideas of primary qualities are patterns or images of things that exist
outside the mind in an unthinking substance that they call ‘matter’. By ‘matter’,
therefore, we are to understand an inert, senseless substance in which extension,
shape and motion actually exist. But I have already shown that extension, shape,
and motion are quite clearly nothing but ideas existing in the mind, and that an
idea can’t be like anything but another idea, and that consequently neither they
nor things from which they are copied can exist in an unperceiving substance.
Berkley gives several reasons for objecting the distinction between primary and secondary
qualities, and one of them particularly concerns us here: The claim that some qualities of
reality resemble their mental representations implicitly assumes the possibility to compare
between the two. But how can we compare our mental states to features of the physical
reality if we have no direct access to the external world? The resemblance assumption
cannot be justified. We do know that some mental qualities (like color, sound etc.) differ
from those physical features they represent (electromagnetic waves, air vibrations etc.),
but this is so only because those features are complex and can be analyzed in more basic
3
Berkeley, Principles of Human Knowledge,§ 9.
terms (space and time among other things). Spatial and temporal features on the other
hand seem to be basic, so we tend to assume (as Locke did) that these physical features
resemble their mental representations. But this is only an assumption, based on the fact
that these are simple and basic features. Since in principle there is no way we can
compare between our mental representations of spatial and temporal features (i.e.
distance and duration) to their external counterparts, to which we have no direct access,
we cannot verify this assumption. Actually, since the category of mental states is so
different than the category of physical features, there is good reason to suspect to the
contrary. It would make more sense if the physical spatial and temporal features too
differed from their mental representations, although we cannot say in what way.
5. Limitations on Our Knowledge of Reality
So, the inability to compare mental representations to features of reality leaves us in the
dark about the real qualities of these features: We do not know what physical space (or
time) is like. There is no doubt that some sort of relation, which we perceive as distance
(or duration), holds between any two objects (unlike Kant I assume that space and time
are features of the external world), but the spatial (or temporal) relation we perceive is only
a mental representation of the real thing, the character of which we have no way of
knowing. Therefore the fact that colors, for example, are representations of
electromagnetic waves does not tell us the whole story: waves are analyzed in terms of
space and time, and we do not know what real space and time are like. And this is not
because we lack the right sort of information. This is so in principle. The unavoidable
indirectness of our perception dooms us to be forever trapped in the model of reality our
mind creates for us. The character of reality itself is out of reach.