Answering the Problem of Secondary Qualities

Reid's account of secondary qualities offers an alternative to the Non-Physicality Thesis from Chapter 2. It explains how secondary qualities can be objective without featuring obviously in scientific discussions. Perception alone reveals the existence of secondary qualities but leaves science to discern their natures This chapter answers Frank Jackson's case against counting secondary qualities as objective and relates Reid's secondary qualities to Saul Kripke and Hilary Putnam's work on empirically discovered identities.

Primary and Secondary Qualities in Reid’s Theory of Perception

Reid distinguishes primary and secondary qualities according to their roles in his theory of perception. According to Reid, perceptions are rightly caused conceptions of and beliefs in their objects. Sensations serve as "natural signs" or triggers for perceptions but are in no way constitutive of perceptions. This chapter explains the place of primary and secondary qualities in Reid's scheme, focusing on their role as natural signs, Reid's summary accounts of primary and secondary qualities, and Reid's treatments of various primary and secondary species. Contrary to other interpretations, this chapter shows that Reid regards secondary qualities as objective properties of physical bodies.

Why Direct Realism Needs Objective Secondary Qualities

Which of the three premises of the Problem of Secondary Qualities should we dismiss for the sake of Direct Realism? Surprisingly, the Non-Physicality Thesis. Attempts to reject the Spreading Principle and Observation Claim create more problems than they are worth. This chapter entertains and rejects five approaches to harmonizing Direct Realism and the Non-Physicality Thesis including Behaviourism, Disjunctivism, Adverbialism, and Eliminative Materialism. The Non-Physicality Thesis receives some prima facie justification from scientists, but we should examine the case more deeply before closing the Direct Realism.

A Historical Objection

A final objection to the treatment of secondary qualities as objective, causally relevant, physical properties says that perceived physical properties must resemble the ideas they cause in the perceiver. This approach assumes Indirect Realism (and therefore the falsity of Direct Realism), but it was ubiquitous in Reid’s day. This chapter traces Reid’s rejection of the Way of Ideas as it bears on his defense of Direct Realism and theory of secondary qualities. Although this objection would not be likely to get traction among contemporary philosophers, this chapter presents Reid’s case for historical interest and consistency.

Understanding Reid’s Distinction

This chapter defends the interpretation of Reid put forth in Chapter 4. Reid's primary/secondary quality distinction is epistemic rather than metaphysical, conceptual rather than phenomenological, and causal in a loose and lawlike sense. Since such a reading is at odds with every other reading of Reid on this matter, rival interpretations receive extensive treatment as well.

A Priori Objections

Howard Robinson and Bertrand Russell challenge the treatment of secondary qualities as objective, causally relevant, physical properties on non-empirical grounds. Robinson says that no combination of physical properties can account for the phenomenological aspects of secondary qualities. Russell, similarly, sees secondary qualities as knowable through acquainence, unlike scientific properties. Again, the answer involves a sharp distinction between perceived properties and sensations.

Why Direct Realism?

As the common sense view of perception, Direct Realism rightly stands in a privileged position in relation to rival perceptual theories, Idealism and Indirect Realism. For most thinkers, rejecting Direct Realism would require extensive and unwelcome revisions to many other views. Furthermore, Indirect Realism and Idealism fall short of accomplishing their oft-assigned task of solving the Problem of Illusion.

Conclusion

Direct Realism is worth defending. The Problem of Secondary Qualities is weakest at the Non-Physicality Thesis. This book’s reading of Reid offers an account of primary and secondary qualities that rejects the Non-Physicality Thesis while embracing science. Reid’s theory answers the Problem of Secondary Qualities and remains convincing in the face of objections.

Scientific Objections

Objections to treating secondary qualities as objective, causally relevant, physical properties often focus on a few key cases. This chapter considers and answers five such cases, including the perceived heat of lukewarm water, perceived taste of PTC, colour appearances of bees and pigeons, variability of colour appearances due to environmental factors, and metamerism. In each case, the objection receives an answer that challenges a presupposed correlation between sensations and perceived properties. Curiously, this defense involves a rejection of the traditional Western colour taxonomy.

General Exposition of the Problem of Secondary Qualities

Although objections to Direct Realism may arise from claims about any secondary quality (colour, smell, sound, taste, or heat), such objections typically take a certain form. That form involves three distinct premises: an Obsevation Claim saying that we perceive some quality, a Non-Physicality Thesis saying that the quality does not belong to a physical object, and a Spreading Principle that insists on generalizing the observed case to all perceptions. For Direct Realism to overcome the Probem of Secondary Qualities, at least one of these premises must be false.