John Locke’s Theory of Knowledge
(An Essay Concerning Human Understanding)
by Caspar Hewett
John Locke’s epistemology by Casper Hewitt
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Published in 1690, An Essay Concerning Human Understanding
is the masterwork of the great philosopher of freedom John Locke. Nearly twenty
years in preparation Locke began working on The
Essay in 1670 following a series of philosophical
discussion during which he and his friends decided that “it was necessary to
examine our own abilities, and see what objects our understandings were, or
were not, fitted to deal with.” The Essay is an
attempt to establish what it is and isn’t possible for us to know and
understand. “My purpose” Locke says, is “to enquire into the origin, certainty,
and extent of human knowledge; together, with the grounds and degrees of
belief, opinion, and assent.” The aim thus is not to achieve certainty, but to
understand how much weight we can assign to different types of knowledge.
The Essay
is divided into four books, the first three laying the foundation for the
arguments set out in Book IV. Central to Locke’s argument throughout the
Essay is the idea that when we are born
the mind is like a blank piece of paper. He says:
Let us then suppose the mind to be, as we
say, white paper void of all characters, without any ideas; how comes it to be
furnished? Whence comes it by that vast store, which the busy and boundless
fancy of man has painted on it, with an almost endless variety? Whence has it
all the materials of reason and knowledge? To this I answer, in one word, from
experience: in that, all our knowledge
is founded; and from that it ultimately derives itself.
What Locke is talking about here is the content of the
mind, not its abilities.
It is important to highlight this as the notion of the mind as white paper (or
as a blank slate to use another popular metaphor) is one that is still
contentious today and different people mean different things by it. Locke
clearly believes that we are born with a variety of faculties that enable us to
receive and process information (the senses, memory, our ability to use language,
explored in some detail in Book III of the Essay)
and to manipulate it once we have it, but what we don’t have is innate
knowledge or ideas.
Book I of the Essay, Of Innate Notions
is dedicated to refuting the hypothesis that we are born with imprinted or
innate ideas and knowledge, something that puts him at odds with the thought of
Descartes. But it is not just Descartes that he is refuting here. At the time
it was widely thought that certain ideas and principles were imprinted on human
beings from birth and that these were essential to the stability of religion
and morality and I think this is one reason why Locke spends so much time
debunking the notion of innateness. But there is much more to it than that.
Locke believed deeply in humanity. He was not a secular thinker, in fact he was
a devout believer in God, but he thought that the God-given faculties we
possess, especially the ability to reason, gave us a unique place in nature
which we should take full advantage of. Locke was a political animal, intimately
involved in the changes taking place in England at the time, and a great
believer in individual freedom. His was a political project and his interest in
the mind had a practical purpose behind it – he wanted to transform society and
organise it in a
rational way. His rejection of innate ideas was intimately linked to this
project for it is all too easy to claim all sorts of principles as innate in
order to maintain the status quo, meaning that people “might be more easily
governed by, and made useful to some sort of men, who has the skill and office
to principle and guide them. Nor is it a small power, it gives one man over
another, to have the authority to be the dictator of principles, and teacher of
unquestionable truths; and to make a man swallow that for an innate principle,
which may serve his purpose, who
teacheth them.”
Let’s examine his argument.
Consider for example the simple notion that it is not possible for something to
both exist and not exist. Locke argues that if such a proposition were innate
then every person in every period of history would know and understand this,
but this is clearly not the case. If such truths were ‘imprinted’ on us all
then we would expect that “children
and idiots” would not only be fully
aware of them, but also be able to articulate them. For Locke it makes no sense
to imagine both that ideas or knowledge are innate and that we do not know
them, thus in his own words: “It seems to me a near contradiction to say that
there are truths imprinted on the soul, which it perceives or understands not;
imprinting if it signify anything, being nothing else but the making certain
truths to be perceived.” He goes on to take up the suggestion that innate
propositions are only perceived under certain circumstances. The crux of his
argument is that once we start to think in this way it becomes unclear what is
meant by innate ideas at all – if we are not all aware of them nor able to
perceive them can they really be described as innate? Accepting such a view
would make it impossible to distinguish between innate ideas and new ideas that
we discover.
He also takes
up at some length the claim that innate propositions are discovered when people
come to use reason. For Locke it makes no sense to describe a truth that is
discovered through the use of reason as innate and he constructs a careful
argument to back this up, investigating and refuting different interpretations
of the claim. I do not have space here to go into too much detail here, but Locke
goes on to reject the claim that there are innate practical moral principles or
that we are born with innate ideas of God, identity or impossibility.
Book II of the Essay, Of Ideas, lays out
how human beings acquire knowledge, beginning by making a clear distinction
between different types of ideas. There are simple ideas which we construct
directly from our experience and complex ideas which are formed by putting
simple (and complex) ideas together. Locke divides complex ideas into three
types which he describes as ideas of modes, substances and
relations. Modes are
“dependences on, or affectations of substances” and relations. Thus they are
things that depend on us for their existence, including things as diverse as
the ideas of gratitude, rectangle, parent, murder, religion and politics. Substances are things in the material
world that exist independently, including what we would generally describe as
substances such as lead and water, but also including beings such as God,
humans, animals and plants and collective ideas of several substances such as
an army of men or flock of sheep. Relations
are ideas that consist “in the consideration and comparing one idea with
another.”
Locke proposes
that the mind puts ideas together in three different ways. The first is to
combine simple ideas to form complex ones. The second is to bring two or more
ideas together and form a view of them in relation to each other. The third is
to generate general ideas by abstracting from specific examples. Thus we ignore
the specific circumstances in which we gain a particular piece of knowledge,
which would limit its applicability, and generalise so that we have some rule or idea
that applies in circumstances beyond our direct experience. This interpolation
and abstraction is important in a number of areas (morality for example) but is
of course essential to science, and Locke’s familiarity with the mechanical
philosophy provided part of the reason for emphasising this way in which we generate ideas.
He goes on to discuss how sensation and reflection give rise to a number of
kinds of ideas, including moral relations and ideas of space, time, numbers,
solidity, identity and power.
By far the longest chapter in Book II is a
discussion of power and this is particularly interesting in that it provides an
opportunity to explore the notions of free will and human agency, which lie at
the heart of Locke’s political project.
Here we are not talking about power in the sense it is used in physics
(the rate at which energy is used) nor about the power one person exerts over
another, but rather in a much more general sense of an ability to make a change
(active power) or receive a change (passive power). For example “fire has a
power to melt gold … and gold has a power to be melted … the Sun has
power to blanch wax, and wax has a power to be blanched by the Sun.” Thus
“the power we consider, is in reference to the change in perceivable ideas.”
Locke’s primary
interest in power is, unsurprisingly, not related to substances in general, but
is in the abilities of human beings, in particular the powers or faculties of
the mind such as liberty, will and desire. He defines
liberty as “a power to act or not to act, according as the mind directs”
whereas the will is a “power to direct the operative
faculties to motion or rest in particular instances,” and argues that
desire is an uneasiness “fixed on some
absent good, either negative, as indolency to one in pain; or positive, as
enjoyment of pleasure.” He is careful to distinguish between these powers and
the person (the agent) who possesses
them, for these faculties are not “real beings in the soul” that can perform
actions – only the person acts. In a similar vein he argues that one power
cannot operate on another, “it is the mind that operates, and exerts these
powers; it is the man that does the action, it is the agent that has the power,
or is able to do.”
Thus for Locke the idea
of free will is nonsensical – a person can be free “to think, or not to
think; to move, or not to move, according to the preference or direction of his
own mind,” but the will cannot, for
it is simply one of the faculties of a person – the will does not think, nor
can it choose a course of action, thus how can it be free? In order to
emphasise the distinct nature of the powers discussed he points out that “there
may be thought, there may be will, there may be volition, where there is no
liberty.” For example a man falling into
water from a height “has not herein liberty, is not a free agent” since,
although he would prefer not to fall he is not in a position to act on that
preference. Similarly a man hitting a friend due to a convulsive movement of
his arm would not be considered by anyone to have liberty in this as it is out
of his control – he has no choice in the action.
Locke’s discussion of identity is also
interesting in that it explores what we mean when we think of something
retaining a particular identity. If we are dealing with an inanimate object
this is quite straightforward, we simply have to ask whether it consists of the
same matter, but if we are considering a living being things are not so
straightforward: “a colt grown up to a horse … is all the while the same …
though there may be a manifest change of the parts.” Here identity is
associated with some continuity of life of the being in question rather than it
consisting of the same matter. When it comes to humanity the question of
identity becomes further complicated and Locke makes an important distinction
between a human being (‘man’) and a ‘person’. The identity of a human being is
the same as that of any other animal, defined by “participation of the same
continued life,” but a person is “a
thinking intelligent being, that has reason, and reflection, and can consider
itself as itself, the same thinking thing in different times and places.”
Book III of the Essay, Of Words, is
central to Locke’s epistemology or theory of knowledge. He explores the
intimate connection between the names we give to things and ideas and,
following the arguments detailed in Book II, links language and ideas directly,
claiming that most words “are names of ideas in the mind.” He does deal with
other types of word, such as particles that “signify the connexion that the
mind gives to ideas, or propositions, one with the other” but his focus is on
words that represent ideas in the mind. Thus most words can be classified
according to the same categories as ideas were in Book II; words for
substances, modes and relations.
He emphasises that when we use words
they always represent the ideas the person speaking has in his or her head,
which are not necessarily the same as the ideas associated with those words in
the mind of the person listening. However, language is such that people
generally assume they mean the same thing when they use a particular word and,
further, “often suppose their words to stand also for the reality of things.”
This leads him to explore different types of words, how we understand them, and
how we use them to increase knowledge. He points out that most words are
general terms arguing that if this weren’t the case language wouldn’t be much
use for improving knowledge, for while knowledge is “founded in particular
things” it “enlarges itself by general views.” He sees words as becoming
general “by being made the signs of general ideas” and it is here that the
intimate connection between words and ideas is key.
Locke claims
that it is not possible to define the names of simple ideas, only complex ones,
since simple ideas are rooted in the things that we sense and can only be named
by reference to the things themselves: “Simple ideas … are only to be got by …
impressions, objects themselves make on our minds.” He cites the problem of
trying to define the meaning of the word light to a blind man as an example.
Without the sense of sight it is not possible to understand any definition put
forward in the way a sighted person can. Complex ideas, on the other hand, can
be defined in terms of simple ideas, provided we are equipped with all the
appropriate senses (e.g. sight) for understanding the simple ideas used. For
example a rainbow can be defined in terms of its shape, the colours it consists
of and the order they appear in.
Pointing to
the non-universal nature of words and language, Locke points out that words in
one language do not always have an equivalent in another “which plainly shows,
that those of one country, by their custom and manner of life, have found
occasion to make several complex ideas, and give names to them, which others
never collected into specific ideas.”
Locke also discusses the essence of a sort or species of idea, by
which he means “that abstract idea to
which the name is annexed; so that everything contained in that idea, is
essential to that sort.” He makes a distinction between the nominal and
real essence of a sort.
The nominal essence is the complex idea a word stands for, while the real
essence is the true properties or constitution of the thing we describe by the
word, some of which we may know, but many of which we usually don’t. This
distinction is extremely important to Locke’s overall thesis since the aim of
the Essay is to examine what we can
and cannot know. For Locke the real essence of something is not something we
can ever know, as there will always be some properties, or some behaviour that we are
unaware of. Nominal essences on the other hand will vary from person to person.
For example the “yellow shining colour, makes gold
to children; others add weight, malleableness, and fusibility; and others yet other
qualities …” However, we have to be very careful when we talk of real essences.
For one thing we only suppose their being, without knowing what they are, but
also the real essence of a substance such as gold “
relates to a sort” and thus is related to our abstractions and the
words we assign to them; “our distinguishing
substances into species by names is not at all
founded on their real essences.” Inevitably the way in which we
group substances into sorts or species is based on “their nominal,
and not by their real essences
… they are made by the mind.”
This whole account of essences, and indeed
the deliberate use of the word essence,
represents an important break from the essentialism of the
Aristotelian tradition that Locke was taught in
his youth. Aristotle believed that there are natural kinds, the essences of
which can be organised into a single hierarchical system of classification
which corresponds to the way nature is structured. Locke rejected this claim
entirely. Rather than a unique classification open to discovery by the
scientist Locke thought it useful to classify things in lots of different ways
depending on what one wanted to do. This is quite a profound difference. It
represents an important break with the thinking of the past and in this he was
clearly influenced by natural philosophers such as his old friend and mentor
Robert Boyle. Part of the reason for discussing words in Book III of the
Essay is precisely to break down the
idea of fixed boundaries between species or sorts of ideas. He says “these
essences of the species of mixed modes, are not only made
by the mind, but made very
arbitrarily, made without patterns, or reference to any real existence.” In
this he prefigures Charles Darwin, who needed to dispense with the concept of
fixed species of animals in order to establish the theory of evolution by
natural selection, by nearly 170 years!
It might seem from this discussion that Locke believed
that words never retain a common meaning when they are used by one person
speaking to another, but this is not the case. Locke, the master of common
sense, was well aware that words must sometimes signify the same meaning to
different people for otherwise there would be no communication and language
would be completely useless. However, the more complex the idea signified by
the word, the more likelihood that the word represents a different idea in the
mind of each person who hears or reads it. For the most part Locke sees
language as a tool for carrying out the pragmatic communication necessary in
everyday life. Ordinary people are the creators of language:
“Merchants and lovers, cooks and tailors, have words
wherewithal to dispatch their ordinary affairs; and so, I think, might
philosophers and disputants too, if they had a mind to be clearly understood.”
Book IV of the Essay,
Of Knowledge in General, brings to bear the arguments in the
previous books on Locke’s central question of what we can and cannot know. His
approach is to deal with what knowledge is, how we reach it, what the different
types of knowledge are and how certain we can be of any knowledge we gain. He
defines knowledge in terms of whether or not one idea in our mind agrees with
another (or others), thus it is “the
connexion and agreement, or disagreement and repugnancy of any of our ideas.”
This is significantly different from Descartes’ account of knowledge which
defines it as any ideas that are clear and distinct. Here we can see why Locke
is at such pains to make it clear what he means by ideas and their signs
(words) before defining knowledge and embarking on the central question of the
Essay. He argues that “all that we know
or can affirm concerning any of” our ideas
is, that it
is, or is not the same with some other, that it does, or does not always
co-exist with some other idea in the same subject; that it has this or that
relation to some other idea; or that it has a real existence without the mind
and that “wherever the mind perceives the agreement or
disagreement of any ideas, there be certain knowledge.”
He defines four sorts of agreement or disagreement: identity,
relation, co-existence (or necessary connexion) and real
existence giving the examples:
‘blue is not yellow,’
is of identity. ‘Two triangles upon equal basis, between two parallels are
equal,’ is of relation. ‘Iron is susceptible of magnetical impressions,’ is of
co-existence, ‘GOD is,’ is of real existence.
He distinguishes
between three types of knowledge, which have different degrees of certainty.
The clearest and most certain is intuitive
knowledge, the second most certain demonstrative
knowledge and the third sensitive knowledge.
Intuitive knowledge is
that where “the mind perceives the agreement or disagreement of two ideas
immediately by themselves, without the intervention of any other.” For example
‘white is not black,’ ‘a circle is not a triangle,’ ‘three is greater than
two.’
Demonstrative knowledge
is that where the agreement or disagreement is not perceived immediately, but
rather depends on reasoning –
following a series of steps in the mind, each of which must have intuitive
certainty, to discover the agreement or disagreement of ideas “by the
intervention of other ideas.”
Those intervening
ideas … are called proofs, and where
the agreement or disagreement is by this means plainly and clearly perceived,
it is called demonstration, it being shown
to the understanding, and the mind made see that it is so.
Because of all the
steps involved in achieving this sort of knowledge it is seen as “more
imperfect than intuitive knowledge.” This sort of proof is common in my
discipline of mathematics, but Locke is arguing that this type of reasoning is
valid in all areas of knowledge.
As an illustration I am
going to show you a simple demonstrative proof of one of Locke’s examples: that
if we add the three angles in a triangle together they are the same as two
right angles. I will not use any mathematical symbols as I know this will put
off at least two thirds of my readers, but will rather use a series of
diagrams. The idea, remember, is that each step should have intuitive certainty in order to provide proof of the hypothesis through reasoning and I hope that the example I
have chosen will carry you with it.
First we remind
ourselves that a right angle is the angle we find in a square or rectangle,
looking like a capital ‘L’, see [1] in the diagram below. I am only going to show you
the proof for an acute angled triangle (one with no angles larger than a right
angle), so let’s start with a general acute angled triangle as shown in [2]. If
we take an identical triangle and turn it upside down as shown in [3], then
bring the two triangles together as in [4] then we have the shape shown in [5]
which we describe as a parallelogram. We can see that each of the three angles
a, b, c in our original triangle appear twice in the
parallelogram.
If we look at the top left corner of the parallelogram in [5] (labelled D
in [6]), I can draw a line from there to the
base of the parallelogram to make a right angle with the base as shown in [6].
Now what we have is a right angled triangle on the left and a four sided figure
on the right that can be separated as in [7]. The triangle can be moved over to
the right hand side of the diagram, where, because of the size of the angles it
will fit exactly onto the other figure, making a rectangle, see [9] and [10].
Thus we have demonstrated, by means of diagrams that
the three angles a, b, c in our original triangle, when doubled (two
triangles in [3]) have angles adding up to four right angles (in the rectangle
in [10]). Thus angles a, b and c add up
to two right angles. There are other ways of proving this, but I quite like
this diagrammatic proof by demonstration for its appeal to our intuitive
feeling for shapes and how they fit together.
The last type of knowledge Locke discusses, sensitive
knowledge, is the least certain as it is founded on objects that enter our
minds directly through the senses. Locke is well aware of the doubts associated
with trusting our senses but, ever the common-sense philosopher, argues
strongly that it makes no sense to reject the input we receive from the outside
world. We should accept that things in the external world have a real existence
even if our knowledge of them will always be imperfect:
The notice we have by
our senses, of the existence of things without us, though it be not altogether
so certain, as our intuitive knowledge, or the deductions of our reason …
deserves the name of knowledge.
Continuing on this
theme, Locke claims that it is not possible for us to discover the connection
between what he describes as the primary and secondary qualities of a
substance. The term primary qualities refers to the ‘real’
attributes of a substance, such as its size, shape and motion while the
secondary qualities are those that we
sense such as colour, taste or sound. The problem is that, while there is no
doubt a connection between these different types of quality, nothing in the
substance itself truly resembles its secondary qualities. It is simply that the
physical attributes of the substance, its primary qualities, have “a power to
produce those sensations in us.” Thus, while arguing that we should trust that
our senses provide real, if imperfect, knowledge of the physical world
(sensitive knowledge), he also severs the connection between simple ideas (in
this case secondary qualities) and reality.
This leads on to a
consideration of probability or
likelihood of truth. We have to accept the lack of certainty associated with
our understanding of the physical world because of our reliance on our senses,
but this does not mean that we cannot make rational judgements about what we
observe. Locke presents an account of probable reasoning which is very similar
to the demonstrative reasoning that generates knowledge. However, not every
step in probable reasoning has intuitive certainty, only a certain likelihood of
truth. Thus when we judge an argument or proposition as true or false we cannot
guarantee that our judgement is correct, only that it is more or less likely.
Therefore there are degrees of such judgement ranging from near certainty to
highly improbable. Locke’s discussion of probable reasoning in the
Essay does deal with things that we can
observe and experience, but his focus is on things beyond our senses including
immaterial spirits such as angels, things too small to sense such as atoms and
life on other planets, which we cannot sense because of their remoteness from
us. However, I want to draw attention to the profound importance of his points
about probable reasoning if we are to have a true appreciation of the strengths
and limits of the scientific method.
This search for knowledge through probable reasoning
is one way of thinking about what the sciences are all about –when we assess a
theory or hypothesis we balance probabilities. What is more likely? Why? At
every step of an argument we should be weighing up our level of certainty. In
general, because we are rarely dealing with ‘intuitive certainty’, the more
steps, the less certain we are of our conclusions. However, the more
experiments and observation we can perform related to each step to confirm or
refute our assumptions, the more certain we can be. This is very important to
appreciate and unfortunately is not appreciated by a lot of scientists! It is
also a huge problem for the sciences of humanity – human beings are so complex
and so different from one another that it is surprisingly difficult to
construct general arguments about humanity that hold up to this kind of
scrutiny.
So, what can and can’t we know? Like
Descartes, Locke argues that we can be certain of our own existence, this
falling into his category of intuitive knowledge, and we have “a demonstrative
knowledge of the existence of God.” Regarding “the real, actual existence
… of anything else, we have no other but a
sensitive knowledge.” However, there are areas of knowledge, such as
mathematics and morality, which are capable of demonstration and thus a high
level of certainty. This is because they are closed systems in which the rules
are created in our minds – they do not depend on input from our senses. He uses
two telling examples: ‘Where there is no property, there is no injustice,’ is
certain
for the idea of property, being a right to any thing,
and the idea to which the name injustice is given, being the
invasion or violation of that right; it is evident, that these ideas being thus
established, and these names annexed to them, I can as certainly know this
proposition to be true, as that a triangle has three angles equal to two right
ones. Again, ‘no government allows absolute liberty’: the idea of government
being the establishment of society upon certain rules or laws, which require
conformity to them; and the idea of absolute liberty being for anyone to do
whatever he pleases, I am as capable of being certain of truth in this
proposition, as of any in mathematics.
However, it is difficult to establish
certain truths in ethics because of the complexity of moral ideas and this
where the discussion of language in Book III becomes most pertinent: Locke
draws attention to two ‘inconveniences’ that are a consequence of this complexity.
First, that the words we use, the ‘names’ assigned to moral ideas, are less
precise than those of, say, mathematics, thus the idea carried in one mind by a
certain word may differ from that in another mind. Secondly, that it is
difficult for the mind to remember precisely all the relationships between
different ideas and thus, especially when several complex moral ideas are
involved, it can be very difficult to decide on the agreement or disagreement
of ideas being compared (which, remember is Locke’s definition of how we come
to knowledge). Morality does not have the advantage that mathematics has of
being able to use diagrams (and precisely defined symbols) which allow you to
review each stage of a demonstration with ease.
Following this train of thought, Locke moves
on to the extent of our knowledge “in
respect of universality,” arguing that only abstract general ideas can
provide any sort of universal knowledge:
If the ideas are abstract, whose agreement
or disagreement we perceive, our knowledge is universal. For what is known of
such general ideas, will be true of every particular thing, in whom that
essence, i.e. that abstract idea is to be found: and what is once known of such
ideas, will be perpetually, and for ever true. So that as to all general
knowledge, we must search and find it only in our own minds, and ‘tis only the
examining of our own ideas, that furnishes us with that.
Only truths belonging to abstract ideas are
eternal “as the existence of things is to be known only from experience.” This
further underlines Locke’s arguments concerning morality for “the truth and
certainty of moral discourses
abstracts from the lives of men, and the existence of those values in the
world, whereof they treat.”
He also warns against confusing ideas with
the words we assign to them as “the examining and judging ideas by themselves,
their names being quite laid aside” is “the best and surest way to clear and
distinct knowledge.”
In Chapter X Locke lays out how we can be
sure of the existence of God. I will not go into the details of his argument
here, but do think it of interest to pick out two key points that lie at the
heart of his reasoning and which I think are philosophically flawed. The first
is that it is inconceivable that there was ever a time when there was nothing –
for this he appeals to our intuitive certainty that “bare nothing” could not
possibly produce any real being. Thus there must be an eternal being “since
what was not from eternity, had a beginning, and what had a beginning, must be produced
by something else.” He goes on to reason that “the eternal source then of all
being must also be the source and original of all power; and so this eternal being must be also the most
powerful” and also must be a “knowing intelligent being,” as there is no
other way that humans, who are knowing intelligent beings themselves, could
have come into existence:
It being as impossible, that things devoid
of knowledge, and operating blindly, and without any perception, should produce
a knowing being, as it is impossible, that a triangle should make itself three
angles bigger than two right ones. For it is as repugnant to the idea of
senseless matter, that it should put into itself sense, perception and
knowledge, as it is repugnant to the idea of a triangle, that it should put
into itself greater angles than two right angles.
Like the earlier discussion of species this
argument bears an interesting relationship to ’s theory of evolution by natural
selection, which did not come along for another 170 years. provides us with an alternative: his
theory explains how a blind process can generate sense, perception and
intelligence. I discuss this at length elsewhere, but thought it worth drawing
attention to while dealing with Locke’s ideas. However, as with any of the
great thinkers, it is also worth remembering when Locke was writing and not
take it out of context. Locke believed in questioning everything and in not
accepting the authority either of the past or of the clergy. He wanted people
to rely on their own judgement
and reasoning which is precisely why he constructs an argument to
justify believing in God, and that is interesting in its own right. I will
return to this theme at the end of the chapter.
Having found the bounds of human knowledge
and certainty Locke turns to the various degrees of probability or likelihood
of the truth of an idea. This is the area of human knowledge where, in the
absence of certainty, we have to apply our
judgement. Here our minds have to take ideas to
agree or disagree or take some proposition to be true or false “without
perceiving a demonstrative evidence in the proofs.”
The highest degree of probability follows
from what our own and other people’s “constant observation has found always to
be after the same manner,” for example that fire burns. We cannot prove that
fire burns in all circumstances, but our experience and what we know of the
experience of other people gives us no reason to doubt that it will continue to
do so in conditions we have yet to come across. These probabilities rise near
to certainty and we generally don’t distinguish between them and certain
knowledge. The second degree is when “my own experience, and the agreement of
all others that mention it, a thing to be, for the most part, so: and the particular
instance of it is attested by many undoubted witnesses.” This degree of
probability, while less certain than the first degree, we tend to have
confidence in, and will generally be willing to act on as if it were fact. The
third degree, which is of course the weakest, is based on what Locke calls
‘fair testimony.’ This is when we are told that something, confirmed by
witnesses, happened at a certain time and place and, having no contradiction or
reason to disbelieve the account, we believe it.
Locke draws attention to the difficulties
associated with probabilistic reasoning, particularly when something
contradicts common experience, or when different witnesses or histories give a
different account of events. However, we should always try as best we can to
assess the likelihood of an account for ourselves and should not fall into the
trap of discounting something which is counter to our own experience – this may
simply reflect that our own experience is limited! This is good advice for any
scientist as much of science seems at face value to contradict common sense
(does the Earth appear flat or curved to you?) – it is only when we investigate
further (experiment, observation) or look at the right scale that the
properties or behaviour
of an object are revealed.
In the closing chapters of the Essay Locke makes a number of points
about reason, faith and judgement
which stand today as useful guidelines for how we should approach
knowledge. He urges us to trust our own judgement and to consider the probability of
any proposition for ourselves. He makes the interesting point that repetition
of a single testimony should give it no more weight than if it were only heard
once. His point here was primarily aimed at the word of the ancients, and had a
bearing on the general point about rejected authority and trusting oneself. It
is also another point highly relevant to the modern era, especially in this age
of instant messaging and the web, where a single testimony can be repeated a
million times extremely rapidly without any verification of facts or truth. It
is always worth distinguishing between a variety of sources confirming
something and a number of sources repeating the same rumour!
Locke is explicitly against artificially formalised types of
reasoning, attacking at length the use of syllogism, a highly formal type of
argument favoured
by Aristotle and his followers. Rather he makes the case for
argument from judgement as the only
sort of argument that brings true instruction and advances us in our way to
knowledge. He describes it as “the using of proofs drawn from any of the
foundations of knowledge, or probability.” Its validity arises from it
relying solely on reason, not on respect
for the reputation of some kind of authority, nor on accepting an argument simply
because we do not know a better one.
Locke makes a point of refuting the idea
that reason is opposed to faith, claiming that faith can never convince us of
anything that contradicts our knowledge and arguing that, except in the case of
divine revelation, we should always look first to our own reason.
Thus anything worldly and open to our own deduction,
observation, experiment or experience must always be a matter of reason. The
only times where it is appropriate to resort to faith alone is in areas not
open to our enquiry such as whether there is an afterlife or whether angels
exist.
C J M Hewett, November 2006
Source
Locke, John (2004) An Essay Concerning Human Understanding,
Penguin Classics
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