This post continues the analysis of Locke’s observations on qualities.
Section 17: Locke reinforces the point that primary qualities exist within the objects themselves, while the secondary qualities do not. If you were to take away a person’s sensory capabilities, the secondary qualities would no longer be perceived by that person, but the primary qualities would always remain.
Section 18: Locke uses the example of ‘manna’ (a sweet juice extracted from plants). When the manna causes a sickness, people readily accept that the manna has reacted badly with a person’s stomach, so the quality is in the manna itself. If we accept that, why don’t we also accept that sweetness / whiteness work in the same way? These are require that the senses act in a certain way based on the secondary qualities of the manna.
Section 19: In another example, Locke talks about a red and white rock. We see the red during the day but nothing at all at night. However, nobody would claim that the rock has changed its form from day to night. Rather, the secondary qualities are derived from the primary qualities. In this case, Locke claims that the rock’s texture is what gives it colour.
Section 20: In a third example, Locke indicates that a crushed almond tastes different from a whole almond, which indicates that when the primary qualities are changed, this has an effect of altering the secondary qualities.
Section 21: To demonstrate how secondary qualities rely on the person perceiving the quality, Locke uses the example of a container of water that feels cold to one hand but warm to another. This proves that the secondary qualities cannot be in the water alone. The perception of warmth has already been confirmed as a secondary quality. The difference in warmth comes about from the fact that the motion of particles in each hand is different, which gives rise to different sensations when the hands are put in contact with the water.
Section 22: Locke sums up his argument so far. The primary qualities are always within the object itself, while the secondary qualities come about from the powers of the primary qualities as they combine together in different ways. We can also ask whether our ideas resemble the qualities in question.
Sections 23/24: Locke returns to discussing his third type of quality, one that he calls a ‘power’. A power has the ability to cause a change in other objects, such as the way in which fire causes lead to melt. A power is similar to a secondary quality in that both rely on the properties of the observer. Locke would suggest that boiling a pot of water over a fire is an example of a power at work.
Section 25: In general, people group secondary qualities with primary qualities, but this is incorrect. We are better off grouping the secondary qualities with the powers. Locke turns to his ‘resemblance theory’ to support this notion. Neither the secondary qualities nor the powers have any resemblance to the qualities in the object, so this suggests that the two are more closely related to each other than the primary qualities.
Ultimately Locke wants to show that secondary qualities don’t really exist in objects alone, but rather work in a ‘relative’ way in that they also rely on the presence of someone who can perceive the quality. In other words (to use more modern language), the secondary quality is a disposition in an object to produce a certain kind of sensory experience. Locke describes secondary qualities as ‘mere powers’ or ‘powers barely’.
Final Thoughts on Locke: Based on Locke’s approach, one could argue that secondary qualities actually rely on three things: (1) a disposition in an object to act in a certain way (a rock that produces a red colour), (2) a medium via which the effect can be produced (ie colour requires light to be shining), and (3) someone to perceive the effect.
This may work differently with the non-visual senses (smell, taste) as this relies less on a medium to convey the quality. Alternatively, you could argue that item (3) – perception in the observer – pre-assumes the existence of certain states, such as daylight. Colour could be perceived as another primary quality, as this does exist in the object itself. One could question whether both Locke and Boyle give too much importance to visual qualities. Why should a visual aspect be considered primary while an audible one is seen as secondary?