The Primary-Secondary Quality Distinction

This is another article (very lightly edited here) I wrote and posted on the Internet in 2009.

In the Appendix of the second edition of Introduction to Objectivist Epistemology Ayn Rand says the primary-secondary quality distinction (PSQD) is invalid. “The primary-secondary quality distinction is a long philosophical tradition which I deny totally. Because there isn't a single aspect, including length or spatial extension, which is perceived by us without means of perception. Everything we perceive is perceived by some means.” 

Of course, everything we perceive is perceived by some means, but the famous supporters of the PSQD, like Galileo Galilei and John Locke, did not deny this. Rand’s argument was against a straw man. 

Primary qualities are those of objects regarded as independent of any observer, such as solidity, extension, motion, number and figure (shape). They exist in the object self-contained and do not rely upon anything external. Secondary qualities are those that produce sensations in observers, such as color, taste, smell, and sound. A sensation or perception can differ due to different perceptual systems, e.g. color-blindness versus normal color vision, or what is external to the object, e.g. light conditions. The powers an object has to produce sensations in us depend on its primary qualities (John Locke, ECHU, II, VIII, 10). 

Rand says, “The primary-secondary distinction in fact starts from the idea that that which we perceive by some specific means is somehow not objective.” I disagree if “not objective” was intended to mean “subjective” in her vocabulary.  Using her intrinsic-objective-subjective trichotomy, the PSQD says that primary qualities are intrinsic rather than objective. Secondary qualities are objective in this regard. Indeed, next she says: “Now you can properly distinguish that which is in the object from the form in which you perceive that quality. But that isn't the same thing as saying color is a secondary quality but extension is a primary quality.” I agree it isn’t the “same thing”, but such distinguishing is what the PSQD does. 

In Objectivism: The Philosophy of Ayn Rand Leonard Peikoff says the dominant view by philosophers gives only two possibilities in regard to sensory qualities: they are "in the object" or "in the mind." The former is taken to mean qualities independent of man's means of perception; the latter is taken to mean "subjective and/or unreal." Why he says this view is dominant is beyond me, and it isn’t the case for the major supporters. More accurately, the PSQD does not say secondary qualities are solely "in the mind", but that they are not solely “in the object.” 

Locke went on to say that our ideas of primary qualities resemble those qualities as they are in an object, but that is not true of our ideas of secondary qualities. He stated this as a conclusion without further explanation (ECHU II, VIII, 9). He did not use what I regard as a strong argument for the PSQD.  That is the nature of our various senses, something Aristotle noted long ago. According to Aristotle the “common sensibles” are motion, rest, shape, magnitude, number, and unity (De Anima III.1 425a16). (Different translations might use slightly different terms here.) They are apprehended by more than one sense – sight and touch. For example, extension and roundness can be perceived by both sight and touch. What Aristotle called the “special perceptibles” were those grasped by one sense only, e.g. warmth, color, taste, smell and sound. Aristotle did not make the PSQD. He treated all qualities of an object or body as belonging solely to the object or body. However, he gave one of the means to do it. 

Another argument in favor of the PSQD is that primary qualities are measurable or countable, but secondary qualities are not. Measuring decibels or sound wave frequency or amplitude is not measuring the sensation of sound. Measuring light wave frequency or amplitude is not measuring the sensation of color. 

In The Evidence of the Senses David Kelley makes a PSQD, but not in the same manner and for the same reasons as Locke did.  Kelley says primary qualities are macroscopic and extensive, while secondary qualities are microscopic and intensive (p. 114-15, hb). This macroscopic-microscopic difference is not about the qualities of an object intrinsically; it is about our knowledge. Primary qualities as physical attributes exist at the microscopic level, too. “[W]e find that certain dimensions can be explained by reference to the macroscopic attributes of objects. With other dimensions, however, we cannot find the intrinsic feature of the object itself, to which the senses are responding, unless we proceed to the microscopic level” (p. 116).  It may be a bit clearer to the reader to substitute “features” for “dimensions.”  

"The perception of size, shape, position, motion, and number seems to require enough perceptual integration to isolate as units the objects which possess these attributes.  …  Thus it seems that the awareness of secondary qualities first occurs at the level of sensations, but the awareness of primary qualities require the perceptual level and necessarily includes some awareness of secondary qualities" (p. 113) “Moreover, since the primary qualities are macroscopic, it is easy to measure them as they are apart from the forms in which we perceive them” (p. 117).  

Kelley also makes an intrinsic–relational distinction between primary and secondary qualities (p. 110, 111, 117, 231). At times Rand described the relationship of consciousness to existence as “objective.”