General Philosophy Lectures HT 2009

THE DISTINCTION BETWEEN PRIMARY AND SECONDARY QUALITIES

When you look at tomato (say) it appears red and round. Are the qualities (or properties) of redness

and roundness qualities which the tomato actually has, independently of your perceiving it?

John Locke suggested that the qualities that we perceive can be distinguished into two kinds:

primary and secondary qualities, such that secondary qualities “are nothing in the objects

themselves but powers to produce various sensations in us by their primary qualities, viz by the

bulk, figure, texture and motion of their insensible parts.” Our ideas of primary qualities resemble

the qualities in the objects, while our ideas of secondary qualities do not resemble whatever causes

our ideas of them.

Primary Qualities: figure, extension, motion/rest, solidity/bulk (mass), number, texture

Secondary Qualities: colour, sound, taste, smell

(Note that these lists vary a little in different parts of Locke’s work.)

There are three key claims being made here:

1) Secondary qualities are powers;

2) Secondary qualities are causally dependent upon primary qualities;

3) Our ideas of secondary qualities do not resemble the causes of those ideas, while the ideas of

primary qualities do resemble a quality in the object.

Locke seems to think that the distinction can be upheld with two general lines of argument:

common sense and science (see below). He gives several examples to illustrate the distinction

(although some commentators consider these to be arguments for the distinction).

Here are some of them:

i) Pounding an almond changes the secondary qualities in virtue of affecting only the primary

qualities (to support (2) above).

ii) A bowl of tepid water feels hot to one hand (which has been in cold water) and cold to

another (which has been in hot water). This ‘illusion’ is different to an illusion concerning

primary qualities.

iii) When you burn your finger on the fire, you don’t presume that the pain you experience is in

the fire, so it is not counterintuitive for the colour not to be in the fire either.

Sophie Allen 1/2009

General Philosophy Lectures HT 2009

Some History

This is probably one of the most famous versions of the distinction (it was made by Locke in 1690),

but it is not the earliest (in fact the distinction between kinds of properties goes back to the Greek

atomists). Slightly different versions of the distinction had already been made by Galileo, Gassendi,

Boyle, Newton, Descartes and many other Enlightenment philosophers and scientists.

To understand the importance of this distinction, it is useful to know something of the prevailing

scholastic view (derived from Aristotle) about the nature of qualities we perceive. For the

scholastics, all qualities are real and exist independently of the mind. So if you see a red tomato, the

redness of the tomato exists independently of your perception of it, as does the roundness of the

tomato, its taste, smell, texture, size, shape and so on. Moreover, your ideas of these qualities

‘resemble’ the qualities in the objects themselves.

Some Science

Locke was a strong supporter of Robert Boyle’s theory of corpuscular mechanism. Boyle claimed

that the natural world could be explained in terms of the mechanical behaviour of insensible

particles (known as corpuscles). Causality is a matter of impact, which is a matter of primary

qualities not secondary ones; so everything which happens must do so in virtue of primary qualities.

Note that Locke was not an uncritical adherent to Boyle’s account of nature, and that Descartes had

a version of the distinction between primary and secondary qualities while holding a plenum theory

of nature (the view that matter is infinitely divisible), so the two theses of corpuscularism and the

primary and secondary quality distinction are independent.

Note also that this discussion is not purely of historical interest. One might wish to maintain some

version of the distinction in conjunction with a contemporary scientific worldview (eg materialism,

physicalism etc.). The basic thinking behind the distinction (scientifically speaking) is that one does

not have to postulate distinct (mind-independently existing) entities to account for some of the

qualities we perceive as being in the world; science would be more parsimonious (invoke fewer

entities).

Criticisms of the Distinction

In general, there are two strategies with which to criticise the distinction: One can criticise a

particular way of making the distinction; or attack the distinction itself and argue that primary and

secondary qualities are all of the same type, either mind-dependent (Berkeley) or that they are all

mind-independent (Armstrong)).

Sophie Allen 1/2009

General Philosophy Lectures HT 2009

a) Berkeley’s (misguided) objection that one can have illusions concerning primary qualities as

well as secondary ones.

b) How can we conceive of primary qualities apart from secondary qualities? This becomes a very

serious objection for someone who (like Locke) was attempting to combine empiricism and

materialism.

c) The problem of resemblance: nothing can resemble an idea but another idea (Berkeley again). It

is a category mistake to treat idea of primary qualities as resembling primary qualities.

Can this objection be avoided?

d) One can criticise which qualities Locke has on his lists. Could there be an updated list? How do

we find out which the primary and which the secondary qualities are?

e) Is this an ontological distinction or an epistemological one? ie Is it about what there is in the

world, or what we know about? (NB For some philosophers what there is is what we (can) know

about; that is, we can’t make claims about what exists if that goes beyond what we could know

about (recall some of the anti-realist responses to scepticism).)

Alternative Views

Two main alternative views to the primary and secondary quality distinction have been proposed:

1) Berkeley: Since what Locke says about secondary qualities also holds for primary ones, all

qualities are mind-dependent. (Note that Berkeley reads Locke as saying secondary qualities are

‘nothing but powers’ or as ideas in the mind, which is usually regarded as being mistaken.)

2) Armstrong: All qualities are mind-independent; that is, secondary qualities exist independently

of the perceiver just as primary qualities do and are real properties of material objects. We can pick

out determinate colours without knowing the nature of the determinable physical quality of colour.

Note that Armstrong uses some of the same arguments that Berkeley does.

Sophie Allen 1/2009