Knowledge Is Ultimately Sensed
Classic Philosophical Questions Part 5 - Knowledge
John Locke, from the An Essay Concerning Human Understanding
Kem Stone - 19 October 2007
While many of the editor’s choices in this volume are a bit curious, there is no question that this excerpt from
Locke is one of, if not
the most definitive argument for empiricism in modern philosophy.  Locke’s idea of the
mind as a “blank slate” that is furnished with ideas only through experience is a concept that even those who have
never read Locke are familiar with.  His argument against rationalism is forceful, and his argument in favour of
empiricism is even stronger.  I am much more inclined towards this position than that of Descartes, yet because I
remain essentially a sceptic I will point out whatever weaknesses I perceive in Locke’s arguments.

The Introduction to
An Essay Concerning Human Understanding lays out Locke’s purpose in making this
inquiry, which is not only to refute rationalism as the proper source of knowledge but to defend knowledge itself
from scepticism.  Locke does not deny that humans have a severely limited understanding of the cosmos, but he
does not believe that the capacity of that understanding is nothing.  By examining how far this limited
understanding of ours actually can extend, we can boast of actual knowledge regarding these concepts and leave
the rest to the sceptics.

Locke is disturbed by those who, in the face of the vastness and complexity of the universe, throw up their arms in
defeat and decide that we can know nothing at all.  Locke analogises this to a servant who will not attend his
business by candle light because he does not have broad sunshine, or a man who will not use his legs because he
lacks wings to fly.  We may have very little to go on, but it is enough to get us started.  The important thing is to
know where our inquiries must stop, and not risk going further for fear of losing everything we have already
gained.  “Thus men, extending their inquiries beyond their capacities, and letting their thoughts wander into those
depths where they can find no sure footing, it is no wonder that they raise questions and multiply disputes, which,
never coming to any clear resolution, are proper only to continue and increase their doubts, and to confirm them at
last in perfect scepticism.  Whereas, were the capacities of our understandings well considered, the extent of our
knowledge once discovered, and the horizon found which sets the bounds between the enlightened and dark parts
of things, between what is and what is not comprehensible by us, men would perhaps with less scruple acquiesce
in the avowed ignorance of the one, and employ their thoughts and discourse with more advantage and satisfaction
in the other” (262).

After declaring his purposes, Locke turns to his argument against rationalism, which rests on the assumption that
“there are in the understanding certain
innate principles; some primary notions, characters, as it were stamped
upon the mind of man, which the soul receives in its very first being, and brings into the world with it” (263).  This
idea is one that Locke believes is widely taken for granted, though it is extremely weak because it is based on the
idea of universal consent: that there are some speculative principles that are universally agreed upon by all
mankind.  It will be sufficient to disprove this idea by showing that there are no such principles.

Locke considers two maxims which any rationalist would no doubt grant would be among the innate ideas that are
imprinted on the minds of all rational beings: (1) “Whatsoever is, is,” and (2) “It is impossible for the same thing to
be and not to be.”  It is immediately clear that these propositions do no not have universal assent, and that they
are unknown to a great part of mankind, particularly children and idiots.  In such cases, the mind has no
apprehension or thought of these principles, yet a rationalist would claim that they are nevertheless imprinted in the
mind.  But Locke points out the absurdity of this claim: “For to imprint anything on the mind without the mind’s
perceiving it seems to me hardly intelligible.  If therefore children and idiots have souls, have minds, with those
impressions upon them,
they must unavoidably perceive them, and necessarily know and assent to these truths;
which since they do not, it is evident that there are no such impressions” (264).  If a notion can be imprinted on
the mind and not unknown, then every truth a man comes to know can be considered innate.

I would pause here to consider that this is not such an absurd idea, and that it had in fact been known and
believed for centuries before Locke was even born.  Plato’s theory of recollection is an example of one such
epistemological framework, in which all knowledge is present in the intellect at all times, and that learning is merely
the process of being guided to remember things that the mind has always known.  But most rationalists would
probably not assent to the idea that
all principles are innate, so Locke’s argument is not defeated by these

Instead of falling back on recollection, rationalists attempt to save their argument by answering that children may
not be aware of these principles until they come to the use of reason, at which point they know and assent to
them.  Locke contends that this claim has two possible meanings: Either (A) as soon as men come to the use of
reason they take notice of these native inscriptions, or (B) the use of reason assists men in the discovery of these

If (A) is true, and men take notice of principles such as (1) and (2) stated above only when they come to the use
of reason, there is nothing to separate these supposedly innate principles from the maxims and theorems of
mathematics, which are also not known and assented to until reason is developed.  Furthermore, it makes no
sense to say that reason allows one to discover what one already knows, as reason itself is the faculty for
unknown truths from those already known.  “To make reason discover those truths thus imprinted is to
say that the use of reason discovers to a man what he knew before; and if men have those innate impressed truths
originally, and before the use of reason, and yet are always ignorant of them till they come to the use of reason, it
is in effect to say that men known and know them not at the same time” (265).

The rationalist may answer to this that mathematical theorems can be distinguished from innate principles such as
(1) and (2) because the former require demonstrations before they are assented to, while the latter are assented to
as soon as they are proposed, without any thought at all.  For instance, one must draw and measure the sides of a
right triangle before assenting to the proposition that a² + b² = c², while one would agree that “Whatsoever is, is”
without having to think about it at all.  However, Locke points out that this is just a further demonstration of the
weakness of the rationalists’ argument, as this claim amounts to saying that to know the truths of innate principles
does not require the use of reason at all.  A principle either is known innately
or it requires deduction; to state that
a principle is innate but requires deductive reasoning to be known is a contradiction.

Turning to (B), if the argument is that these principles are in the mind but are not noticed until we come to the use
of reason, Locke asserts that this is both false and frivolous.  First, it is clearly false because these maxims (1) and
(2) are
not in the mind as early as the use of reason, and do not suddenly become known once the mind develops
this capacity.  It is frivolous because this claim amounts to no more than saying that innate principles “are never
known nor taken notice of before the use of reason, but may possibly be assented to some time after, during a
man’s life; but when is uncertain” (266).  And as Locke points out, the same can be said about all knowable truths.

Even if (1) and (2) became known at the precise time when men come to the use of reason, Locke argues, the
claim of (B) would still be frivolous.  “For, by what kind of logic will it appear that any notion is originally by
nature imprinted in the mind in its first constitution, because it comes first to be observed and assented to when a
faculty of the mind, which has quite a distinct province, begins to exert itself?” (266).  Why not claim that men
come to assent to them when they come to the use of speech?  All that (B) amounts to is that the making of
general abstract ideas such as (1) and (2) requires the use of reason, but this has absolutely no bearing on whether
they exist in the mind beforehand.

Locke concludes his argument by confessing that some ideas are in fact in the mind at a very early stage, even
before the use of speech or reason.  However, these ideas are such that prove they are
not innate.  For instance,
a child has knowledge of differences.  Having tasted food that is sweet and bitter, a child knows that sweet is not
bitter.  But it is clear that these ideas do not come through innate knowledge but through the experience of
sweetness and bitterness.

It is this concept—that
experience is the origin of ideas—that Locke turns to after refuting the claim that ideas are
in the mind by innate impression.  Ideas, which are the
materials of thinking, come to us through two distinct
faculties of the mind, sensation and reflection.  Most of our simple ideas come to us through the senses, and
Locke gives a few examples such as yellow, white, heat, cold, soft, hard, bitter and sweet.  Reflection, on the
other hand, is not the sensation of external objects but our perception of the inner workings of our own minds,
from which we derive ideas such as thinking, doubting, believing, reasoning, knowing and willing (268).

In the next section, Locke draws the crucial distinction between
simple and complex ideas.  When we imagine
any object, such as a piece of wax, many simple ideas are combined into this concept, such as its softness and its
warmth.  “There is nothing can be plainer to a man than the clear and distinct perception he has of those simple
ideas; which, being each in itself uncompounded, contains in it nothing but
one uniform appearance or
conception in the mind
, and is not distinguishable into different ideas” (269).  Thus in the above example,
softness and warmth are simple ideas, while the wax itself is complex.

What is so important about this distinction is that our minds have the power to combine simple ideas into an
infinitude of possible combinations, thus allowing us the power to create limitless complex ideas, yet we can
generate new simple ideas
, nor destroy ideas that we already have.  Locke compares this to the cosmological
principle that the atoms and molecules which compose matter can be combined and mixed in numerous ways, but
no new atoms can ever be brought into existence, nor can any existing atoms be annihilated.  A moment’s thought
will reveal the truth of this claim.  “I would have any one try to fancy any taste which had never affected his palate,
or frame the idea of a scent he had never smelt: and when he can do this, I will also conclude that a blind man hath
ideas of colours, and a deaf man true distinct notions of sounds” (269).

All of our ideas, therefore, come to us purely through experience, and our experiences are limited to those five
qualities which come to us through the senses.  Locke admits that there may indeed be other sensible qualities in
the universe that other creatures in other parts of this vast universe may be capable of perceiving, but we are
limited only to five, just as if we lacked one of these senses we would be limited only to four.  Locke has thus
established the source and the boundaries of our epistemological capabilities: knowledge is not innate but comes
purely in the form of simple ideas that we perceive through the senses and combine through reflection, and we can
not know anything about the universe that requires ideas that can not be perceived through the five senses we

Locke’s arguments are indeed very strong, particularly the assertions he makes regarding the origin of ideas and
the distinction between those that are simple and those that are complex.  We most certainly cannot imagine a
simple idea that has never come to us through the senses, and this is a very powerful argument in favour of

The only objection I can find to level against Locke is that the mind is not really a “blank slate” at birth but does in
fact contain certain impressions that have been passed through the evolutionary chain.  Human babies know very
little of course, but they still possess primary instincts such as how to be nursed.  Other animals are born with far
more complex instincts, but whether such impulses can be called knowledge is debatable.  But if the turtle’s
impulse to return to the place of its birth to lay eggs can be called an
idea, it must be granted that this idea is not
learned through experience but imprinted on the turtle’s mind from the time of its birth.

Whatever the case may be, I would certainly grant that at least
most of our knowledge comes through experience,
and this is a far less problematic foundation for our beliefs than supposedly innate, rational principles.