locke's theory of primary & secondary qualities

Sachin Nandha V7DMETDepartment of Philosophy, University of NottinghamLocke’s Theory of Primary & Secondary Qualities

Locke’s Theory of Primary & Secondary Qualities

In this paper I aim to investigate Locke’s theory of Primary and Secondary qualities.

I will take the following line of investigation in this paper; firstly, I will explain and

attempt to firmly understand exactly what Locke meant by Primary and Secondary

qualities. Secondly, I will discuss some of the core arguments Locke puts forward in

defence of his theory. From which I will launch into a potential critique of his theory,

mainly based on the works of Berkeley and will show why his critique of Locke’s

theory, however valid at points, simply is not sufficient to discard the distinction

altogether. I will end the paper by acknowledging that I have assumed the backdrop

to this whole theory to be true – Locke’s representative theories of perception and so

any investigation into it has been avoided as it is beyond the scope of this

investigation.

Before delving into any arguments for or against Locke’s theory, it is important that I

attempt to clarify exactly what Locke was referring to and what he meant by the terms

Primary and Secondary qualities. In simplistic terms Primary qualities are all those

that are measurable by the mind. For example, shapes, sizes, numbers, motion of

objects, positions etc. are all what Locke calls Primary qualities. Secondary qualities,

according to Locke, are all those things, which are not instantaneously or objectively

measurable by the mind, qualities such as colour, sounds and taste.

To take an example, imagine that I am in a room and I see ten chairs. Each chair is in

a certain specific ‘measurable’ position, it has a certain size and shape and are

stationary. They also exhibit a certain colour, each looks slightly different according

to the light reflected on them, their position in relation to my standing will dictate

what parts of the chairs I can see and what I cannot see and their temperatures will

vary (no matter how little) depending on the level of sunlight they are exposed to.

Here I have described Primary and Secondary qualities. Locke believed that material

things interact with our sense organs and, through them, with our minds in ways that

give rise to those states in us, which we call the having of sensations and perceptions.

1


Locke says that these perceptions and sensations are in our mind caused by the

material objects and their powers. For example, if I see a yellow cube, I see a cube,

which has a shape; definite position in space and it is stationary – hence these are all

primary qualities. I also have the sensation of experiencing yellow – hence this is a

secondary quality. I have a combined idea of a cube and of the colour yellow together

to form an overall idea of a yellow cube. What gave rise to my experiencing yellow?

And what exactly does Locke mean then by ‘powers’ objects posses? The cube

possesses the ‘power’ to produce the sensation of yellow; whenever light reflects of

its surface but it cannot be said that yellow is ‘in’ the cube. The ‘power’ of the cube

to produce yellow is grounded in its atomic structure and the relationship it has with

light as it reflects of its surface. If one were to express this in simplistic terms, it

would be said that Primary qualities are all ‘modifications of matter within the bodies’

and secondary qualities are nothing ‘in’ the object themselves but that every object

has a certain ‘power’ to produce various sensations in us by their primary qualities.

Locke’s concept of Primary and Secondary qualities is deeply embedded in his model

of ‘ideas’. Exactly what did Locke mean by the term? Before introducing the

concept of qualities, he first distinguishes between ideas – ‘the word here must be

used in a broad sense – as they are ideas or perceptions in our minds and as they are

modifications of matter in the bodies that cause such perceptions in us, and proposes

to call only the former ideas’. [J.L. Mackie, 1974, Analysis] According to Mackie,

Locke uses a narrow definition of the term ideas; ideas are simply perceptions in the

mind. Lowe [1995] in his commentary of Locke on Human Understanding draws the

following basic schema, which adequately sums up the essay so far:

1. Subject S perceives object O if and only if S has an idea I of O, where S is a

person, O is the external object such as a tree or a house.

Now that we are clear on Locke’s concept of Ideas and his Primary and Secondary

qualities, it is worth considering if he is indeed justified in his beliefs. Locke, when

introducing the distinction picks out what he eventually labels ‘primary qualities’ and

describes them:

‘…as are utterly inseparable from the body, in what estate so ever it be; such

as, in all the alterations…it suffers…it constantly keeps; and such as sense

2


constantly finds in every particle of matter which has bulk enough to be

perceived, and the mind finds inseparable from every particle of matter,

though less than to make itself singly be perceived by our senses.’ [Locke on

Human Understanding, J. W. Yolton, 1965]

Locke’s first point seems to be that when a body is changed or divided, its parts, if

they are big enough to be seen, can still be said to have shape, size and other primary

qualities. Even if the parts become too small for us to perceive, we must still think of

them as having shape, size and so on. It seems that Locke draws on an unfair

comparison between determinate primary qualities and determinate secondary

qualities. The determinate shape, size and so on of a material thing are as alterable as

its determinate colour, in that no matter how one breaks up a material object and no

matter how small it can break down to, it is still thought that it holds some shape, size

and so on. However, it seems equally true that so long as the parts are big enough to

be seen, it or they will still exhibit some colour. Just as a material object will always

be either in motion or rest, so it will also have some temperature, as it will have

colour and so on. It seems strange however that when a thing is broken down to its

sub-atomic levels it can be easily thought to have some size, shape and so on, but not

any colour or temperature. It seems difficult to imagine what a colour of an atom

would be like and yet I can easily imagine its shape and size. Therefore it seems that

if one carries on the distinction to the point where separate particles are no longer

perceivable by the senses, it seems circular to appeal to the fact that the mind will still

give each particle some shape and size, but not, any colour or temperature. If the

mind discriminates in this fashion, then it has already accepted the distinctions

between primary and secondary qualities and hence, this cannot be the evidence upon

which the theory is based. Due to this circular effect, Locke’s first argument for the

distinction is insufficient and so must be discarded.

The second argument that Locke puts forward, one that seems more plausible, is one

where he refers to the causal processes involved in perception. Even though Locke

“waffles” through his discourse, he brings out some strong arguments for the

distinction. Locke according to Mackie [1976] says:

‘…that the sensation effect need not resemble its cause, as we know it does

not when pain is produced by the motion of a piece of steel as it divides our

3


flesh. Similarly, we need light to see the colours; things have no colour in the

dark. But no one, Locke thinks, will suppose that the light produces colours as

qualities of what we call coloured objects’.

Locke seems correct and on secure grounds on this point, indeed it seems far more

plausible that the different surface textures merely reflect different rays of light.

The third argument from Locke draws an analogy between secondary qualities, pain

and nausea. It seems obviously clear that there is nothing like pain or nausea in the

objects that cause them in us. Locke continues down this line to say why should we

suppose that there must be something like colours as we see them, sounds as we hear

them and so on in the objects that produce these sensations in us? There is definitely

some scope here for Locke’s distinction for secondary qualities, in that in virtue of

some basis in an object it has the power to produce in us a sensation whose content is

quite different from that basis. In other words we often have sensations whose

content is very different from that which caused it. This line of reasoning however,

does not give sufficient grounds for supposing that colours, sounds and so on conform

to this pattern whereas, shapes and sizes do not. Indeed it shows that there is room for

something like what Locke calls secondary qualities but fails to show or ground the

line at which Locke distinguishes primary from secondary qualities.

According to Lowe (1995), ‘Locke shows how his theory enables such illusions as our

feeling the same water as hot with one hand but cold with the other’. His theory goes

something like this: if our feelings of warmth and cold arise out of changes in the

motion of tiny nerve cells travelling through our hand, it is easy to see how the

lukewarm water could produce these feelings by speeding up the relevant motions in

the one hand and slowing down those in the other. I feel that this aspect of Locke’s

theory seems feasible, if a little inaccurate but major problems arise out of Locke’s

need to give contrasting examples. He continues to write the remark that ‘figure’ –

that is, shape – ‘never produces the idea of a square in the one hand and of a globe in

the other’. [Yolton, 1965] This remark has led many philosophers to think that

Locke is attempting to say that secondary qualities are prone to illusion but primary

qualities are not. Many philosophers including Berkeley (which I will discuss further-

in the essay) have criticised this notion by giving simple examples of illusion

4


regarding primary qualities such as shape, size and so on and have gone onto say that

there can be no distinction of the type that Locke seems to think.

The arguments that I have discussed so far as Locke’s own, add up to something of a

case for the primary and secondary distinction, but not a very strong one. Locke’s

securest support comes in the form of scientific explanation, which largely came after

Locke’s life, and as a result his theory seems to have had much success. Even though

the scientific community has largely supported Locke’s view many philosophers have

discarded it believing there to be stronger evidence on the other side of the argument

– there is no such distinction as primary and secondary qualities. What are these

objections against Locke’s theory and are they as conclusive as they have been made

out?

There are several arguments directed against Locke’s theory of Primary and

Secondary qualities especially from Berkeley. I have already mentioned Locke’s

example (‘figure’ – that is, shape – ‘never produces the idea of a square in the one

hand and of a globe in the other’) which has led many philosophers especially

Berkeley to think that Locke thought that one could be prone only to illusions of

secondary qualities and not Primary ones. After reading Locke’s essay, it seems that

Berkeley has taken this example out of context and has distorted what Locke was

trying to show. Even if Berkeley had correctly interpreted Locke, his criticism is still

un-important, as Locke’s theory is not dependent on this matter anyhow.

There is a stronger argument against Locke – or so it is often said. It seems that all

qualities (primary and secondary) co-exist or appear as if they are in the same place at

all times. Referring back to the example of the yellow cube, I do not in fact see a

cube and then a sensation of yellow separately; the colour is intrinsically experienced

along with the shape and size. In other words I see and experience the colour and

shape at the same time. Thinking along the same lines it becomes obvious that there is

not a single instance where I experience only a primary quality and not a secondary

one with it, or vice versa. So if this is the actual case then how can Locke remain

justified in his distinction? In short, this type of objection against Locke’s theory

begs the question. It is absolutely true that experience of primary and secondary

qualities occurs simultaneously and so shows that there can be no distinction. But

5


Locke’s aim was to show that the senses cannot be relied upon and so the distinction

was an attempt by Locke to clarify what our senses experience in normal states.

Therefore, to pose an argument which relies on the senses is simply begging the

question if used to discredit Locke as his actual aim was to show the inadequacy of

the senses.

A far more compelling argument against Locke and one that would force Locke to

revise certain aspects of his theory if he were alive seem to gravitate around his notion

that solidity is a primary quality. Is solidity a primary quality, as Locke has said in

his essay? Almost all of the Primary qualities that Locke lists are, in a broad sense,

geometrical ones. Shape, size, texture, motion or rest and number are all only aspects

of, what Yolton [1965] calls ‘spatio-temporal patterning or distribution or

arrangement of stuff’. Each of these are essentially incomplete, there must be

something that occupies some space and not other space. It would be useless to draw

the boundary of a certain shape if there was no difference between what was on the

one side of the boundary and what was on the other. At this point ‘solidity’ enters the

argument. Surely it is solidity that defines any shape. Locke says ‘this is the idea (by

idea he means quality) that belongs to a body, whereby we conceive it to fill space.’

[Locke, ed. Yolton, 1965] Hume in his Treatise, suggests ‘if solidity is just

impenetrability hence the power to exclude other things of the same sort, it cannot do

this job.’ Here, Hume by using ‘it’ refers to Locke’s notion that solidity is a Primary

quality. Locke’s view is that solidity is not only impenetrability or in other words a

power but also the ground of this power, or in other words a primary quality. In

simple terms, Hume is arguing that solidity is neither a primary nor a secondary

quality. The problem that Locke faces is that the quality itself resembles the idea we

have of it. If solidity is the space filling feature, which makes the difference between

body and empty space and enables each body to keep other bodies out, then we do not

have an adequate idea of it, but only the indirect inference of the grounding of a

power which is itself learned from its manifestations. To go back to the example of

the yellow cube may help clarify matters. The cube has a definite shape. Its surface

is composed in such a way that reflected light is perceived by the observer as yellow.

So it can be said that the cube has a certain surface (source of power), which allows

the observer to experience yellow (which is the power). When combined we see the

6


full manifestation of a yellow cube. Can the same be said about solidity? What this

argument leads to is the notion that Locke’s solidity should not have been on either

list, as it is an inferred physical property. Voltage, electrical charge and mass are

other inferred physical properties and are not directly perceived by the senses. As no

inferred physical property can be directly perceived by our senses, so none can be

called primary quality in the sense of an intrinsic feature of material things, which is

also a ‘resemblance’ of some ordinary pre-scientific idea.

As already noted, this does indeed point to a revision needed in Locke’s account of

primary qualities. But this objection still does not show any need to discard the

distinction altogether. It is equally compelling to argue the notion that we need, for a

coherent account of what we perceive some known properties to make the difference

between body and empty space. What is it then that allows us to differentiate between

what’s called ‘space-filling’ properties and empty space? It seems that it cannot be

Locke’s primary qualities. It certainly cannot be physical properties such as solidity

and mass, as we cannot instantly perceive them, then this by default leaves us with

Locke’s secondary qualities. This certainly does look promising. All space-filling

objects have a colour, which is a secondary quality, but is it only colour that allows us

to identify another body? To take an example from Mackie:

‘…if I feel over the surface of a rigid body, say the top, edge and underside of

a table top, not directly with my fingers but with some instrument, such as a

pencil…can I not detect a shape without being aware of any quality that fills

that shape other than the power of impenetrability?’ [Locke, 1976]

Even though impenetrability was only just discarded as a primary quality and pushed

into the realm of physical theory, it does seem like an adequate quality when it comes

to experience. Under Mackie’s example, it does seem clear that it was this power of

impenetrability that distinguished the body from empty space. So it seems that we

have come a full circle and it does seem that solidity the power of which is

impenetrability is indeed some type of Primary quality, hence Locke is justified. Of

course the case still remains that we cannot perceive primary without secondary in

any situation but then this would be begging the question, yet again. Locke whole

theory has been developed to argue the case that we cannot rely upon our senses and

so they must be revised in our minds.

7


This essay has briefly explored Locke’s theory of Primary and Secondary qualities,

through firstly, understanding exactly what it was that Locke meant by Primary and

Secondary qualities. Secondly, have discussed the arguments Locke used to justify

the distinction and pointing out that some were stronger than others and finally to

have explored the criticism facing Locke’s theory. Through this investigation it

seems that Locke did indeed have adequate justification in forwarding his theory on

the basis of a major assumption. This assumption that I have taken consciously

presupposes Locke’s idea of ‘representative theories of perception’, which

distinguishes between the ideas in our minds and any externally real things. While

supposing that our ideas are causally produced by those external things acting upon

our sense organs and through them in to our brains, all the while assuming that we can

speak intelligibly about the resemblances between some of our ideas and those

external realities. It is in the backdrop of this theory that Locke’s theory of Primary

qualities is situated and takes root. Locke believed that it was the Primary qualities of

external objects that gave us some intelligible idea about the external world, while

secondary qualities were the product of the power possessed by the prior. In other

words the primary qualities really are qualities, and are themselves the basis of the

powers to produce the corresponding ideas in our minds, whereas, secondary qualities

are the product of the power whose basis lies in the primary qualities of minute

atomic particles, or in simplistic terms the result of the shape, size and so on, of the

atomic structure of external objects. This theory has been widely criticised by

philosophers but is beyond the scope of this paper – no doubt one for the future.

Even though this backdrop theory of Locke has been taken for granted for the purpose

of this discussion, I feel that it has been at least secured internally within its own

boundaries – that of the theory of Primary and Secondary qualities.

8


Bibliography

1. Lowe, E.J., 1995, Locke on Human Understanding, Routledge Press 2. Mackie, J.L., 1976, Locke’s Anticipation of Kripke, Analysis3. Yolton, J.W., 1965, Locke on Understanding Human Nature, Oxford

University Press

9

locke's theory of primary & secondary qualities

Documents