Locke offers another way to distinguish between the two qualities. When we have the idea of the quality in our minds, we should see whether this resembles the quality in the object. So resemblance becomes the key factor. In the case of primary qualities, when we consider the shape and size of an object in our minds, this does resemble the actual quality in the object, so we can conclude that these are a primary qualities. However, because smell and taste do not resemble anything in the object, this means they must be secondary qualities.
One side-effect of Locke’s theory is that all our perceptions ultimately derive from ideas in the mind. Locke would therefore conclude that all our perceptions of both primary and secondary qualities are indirect. We do not perceive the object directly.
Having presented an overview of Locke’s theories, what are some of the ways we can question the ideas? The best place to start is with the writings of George Berkeley, who also considered the question of qualities and from where they arise. Berkeley rejects any idea of primary and secondary qualities, believing that there is simply a single ‘quality’ that covers all properties. As an idealist, Berkeley asserts that everything exists entirely in the mind and there is no such thing as external matter. Because we can only ever have ideas, an idea can never be nothing but another idea. It cannot be compared to anything else.
Berkeley also asks us to consider the object as we perceive it in our own minds. He believes that when we do ‘see’ in the object in our mind, we include both the primary and secondary qualities. It is not possible for us to visualise the primary qualities on their own. Berkeley suggests that the distinction between primary and secondary is therefore a spurious one.
Although Berkeley’s idea of visualising the object is not entirely persuasive – one could for instance see the shape of a beach ball in one’s mind without having to see the colour – he does provide grounds for us to question the worth of distinguishing between primary and secondary qualities. If ideas are all that we ever have, how can we be certain that primary and secondary qualities exist separately in nature? In both cases, it is simply perceptions that we are dealing with.
However, the view of Berkeley does require you to accept the mind as the ultimate source of all knowledge. As people who interact and live in a world of matter, this is a counter-intuitive proposition to accept. It is hard to see how a mind-based theory could actually be proven, as our senses tell us almost conclusively that we live in a world of matter. Therefore, Locke’s theory is more persuasive in stating that there is a sense in which objects do exist in time and space, and they possess certain qualities that exist independent of any observer. It is difficult to find any reason to argue against Locke’s notion of primary qualities.
Because Locke wanted his theory to have a dualist backing, he thought it necessary to distinguish between the idea in our mind and the object in reality. If we decide to dispense with the dualist angle – which as mentioned above, is difficult to prove – we can adopt more of an approach of the ‘direct realist’. Despite what Locke claimed, we do perceive objects directly. When we see a table in front of us, we perceive the table’s existence without having to form the idea of the table in our minds. If we are walking in a distracted way through a room, we are aware of the table’s existence and will walk around it, but we haven’t developed the idea of the table in our mind. This suggests that objects do not have to appear as ideas in our minds for us to accept the object’s reality in time and space.
Having concluded that objects have a real existence in the world, and are not merely products of the mind, how does this impact the distinction between primary and secondary qualities? One line of argument is that Locke and Boyle give priority to the visual senses. The primary qualities arise due to sight, whereas the secondary qualities arise due to other sensations. What makes Locke and Boyle certain that sight is the ‘king’ of the senses? Someone could equally claim that hearing is the primary sensation, which means everything we hear should be considered primary, while all the other qualities are secondary.
Locke would contend that primary qualities are inherent to an object. Could you not argue that the sound a bell makes when it rings is also inherent to the object? Locke himself conceded that snow would always be white even if there nobody around to observe the snow. So to claim that secondary qualities exist solely in the mind does not seem persuasive. The secondary qualities, such as the ringing bell and the whiteness of the snow, seem as inherent to the object as the primary qualities. This suggests that we can partially agree with Berkeley. There should be no difference between primary and secondary qualities.
We can also question what philosophical benefit we get from maintaining the distinction between primary and secondary qualities. How does knowing that quality X is primary while quality Y is secondary produce any worthwhile knowledge about the world? One possible argument is that primary qualities are more ‘scientific’ in nature, whereas as secondary qualities are less so, as they require the perceptions of an observer. However, this is no longer such a persuasive argument. A machine could be built to detect the presence of sound or smell, and this would rely on scientific principles in order to measure the property. It is difficult to see how secondary qualities are any less scientific than primary ones.
While Locke’s theory of primary and secondary qualities might have been persuasive in the 17thcentury, it is difficult to see how the theory can be maintained nowadays with our advances in science. We should therefore agree with Berkeley in that there is no distinction between two. However, Berkeley’s assertion that the properties exist solely in the mind should also be rejected, as should Locke’s notion of ‘indirect’ perception via ideas. We can be confident that objects exist in reality, and we do manage to perceive them directly. These perceptions apply equally to both primary and secondary qualities, and there is no longer any need to see them as separate constructs.