‘Qualities of things’ are properties of an object that cause an idea to form in the mind of an observer. When we see a red apple for instance, the idea of redness appears in our mind. But whereas the red apple requires someone to actually see the apple in order to perceive the ‘red-ness’, are there qualities that do not depend on perception at all?
To answer this question, I will refer to the theories of John Locke and George Berkeley. Each offers a different interpretation on the subject of qualities. In summary, Locke argues that ‘yes’, we do have a category of ‘primary qualities’ that exists outside of perception. As for Berkeley, being an idealist – someone who only believes in the mind and nothing of external original – he would answer ‘no’. According to him, all qualities are based on perceptions.
Starting with Locke’s theories on qualities, Locke makes a distinction between three types of qualities. The primary qualities relate to size, shape, extension, motion and number (in terms of number of elementary particles). Since these are qualities inherent in the object, they do not require the presence of an observer. Even if you were to split the object into two – even something as small as a grain of wheat – the two resulting pieces would still have the primary qualities of size and shape. Therefore, Locke would be confident that we do have some ‘qualities of things’ that do not require perception in order to be understood.
Locke also recognises ‘secondary qualities’ and a third quality he calls ‘powers’ (which I won’t discuss any further as part of this essay). These are powers in the objects to create a sensory experience in anyone who happens to encounter the object. A smell of a flower or the taste of honey would be two examples. Since these experiences rely on the presence of an observer, Locke would agree that perception is required to understand the quality.
So to summarise Locke’s position, if the quality is a primary quality, this is an inherent part of the object in question, and perception is not required. However, if the quality is a secondary quality, an observer is required in order to experience the quality first-hand.
Berkeley offers an alternative point-of-view. Starting with Locke’s notion of secondary qualities, Berkeley would contend that these exist solely within the mind of an observer and do not require the existence of anything in the external world. As part of Berkeley’s theories of knowledge, an idea can be compared to nothing but another idea. Therefore, when we have an idea in our minds, this tells us nothing about the external world.
As part of Berkeley’s argument, it could be contended that Berkeley is not reading Locke’s position correctly. Locke never stated that secondary qualities exist solely in the mind of an observer. Rather, the quality is a combination of an observer’s perception, plus a unique set of ‘motions’ within the object that creates the disposition to act in a certain way. However, as Berkeley is more interested in arguing for a mind-focused theory, he interprets Locke as meaning that secondary objects are based purely in the mind.
Because of this mind-centric approach, Berkeley does not distinguish between primary and secondary qualities. As everything is just an idea, all qualities should be treated in the same way. As an experiment, Berkeley asks us to consider any object in our minds. If we do this, we will find that we cannot distinguish between the primary and secondary qualities. This is known as Berkeley’s ‘Inseparability Theory’. Therefore, what Locke refers to as primary qualities also exist in the mind of the observer. Therefore, all qualities according to Berkeley require the presence of the observer, and no qualities can be perceived without perception.
The Inseparability Theory can be criticised though. I believe it is possible to consider an object in one’s mind without thinking about secondary qualities. For instance, I can picture a generic shape and size of a flower in my mind, without any thought as to its colour or its smell. So you could argue that Berkeley’s Inseparability Theory is not so persuasive.
Ultimately whether you prefer Locke’s or Berkeley’s theory depends on whether you think the mind is paramount as the source of knowledge. If you answer ‘yes’ – and believe there is no such thing as external matter – then you would agree with Berkeley that qualities do not exist outside of perception. However, if you are more of a realist like Locke, you would agree that qualities can be distinguished between primary and secondary qualities. Primary qualities can in fact be understood independent of perception.
My own conclusion is that Locke’s view is to be preferred. Based on modern science, it is difficult to see how matter and the external world could not exist, and that everything is based on internal sensations. This proposition sounds similar to the ‘brain in the vat’ thought experiments offered in response to Descartes’ Meditations. As such arguments rely on a lot of concepts that are almost science-fiction-like in nature, it’s difficult to see how Berkeley’s ideas can be taken seriously. As a realist, I believe Locke has a more convincing explanation of how we perceive different types of qualities in the world.