Herbert Feigl, The "Mental" and the "Physical": The Essay and a Postscript (1967).
C. Quality versus Quantity.
Another time-honored distinction between the mental and the physical is made in terms of the qualitative and the quantitative. This distinction also is fraught with the danger of various confusions. A prima facie plausible argument maintains that, e.g., the qualities of colors-as-experienced, sounds-as-heard, odors-as-sensed, heat-intensities-as-felt, etc. are undeniably and fundamentally different from the quantitatively measurable wave lengths of light radiation, the frequencies and energies of sound waves, the chemical compositions of odorous' substances, the mean kinetic energies of the molecules, etc. Of course, they are. But the argument misses the essential point. What the physicist measures are quantitative aspects of stimuli or stimulus patterns. These stimuli produce, under certain ("normal") circumstances, certain qualitatively characterizable sensations within the phenomenal fields. The familiar freshman's question, "Is there a sound when on a lonely island, with neither men nor beasts present, a tree falls to the ground?" is quickly clarified by the distinction between the sound waves (vibrations in the air) and sounds-as-heard. The dualistic argument would, however, be strictly to the point if it concerned the distinction between the sense-qualities-as-experienced and the "correlated" cortical processes in the brain of the experiencing subject. These cortical processes could be quantitatively described in a completed neurophysiology. Various more or less localized patterns of nerve currents ("firings" of neurons, etc.) would be the object of a "physical" description. Just which phenomenal qualities correspond to which cortical-process patterns has to be determined by empirical investigation. In our previous discussion of "conseryanda" and "expli-canda" we have not only admitted, but insisted upon, the synthetic character of the statements which formulate these correlations. Reserving fuller arguments for monism again for the final sections, a few preliminary critical observations are in order at this point:
(a) Purely phenomenal descriptions are generally not restricted to a merely qualitative form. Semiquantitative or rank-ordering ("topological") descriptions are possible at least among the qualities within each modality of experience. "My pain is increasing"; "this (sensed) blue is darker than that"; "my embarrassment was worse than any I had ever felt before" -- these examples illustrate semiquantitative singular statements. Universal statements of this form can also be made, e.g., "Purple is more bluish than scarlet." "D is higher in pitch than C." Universal statements of this sort can be organized in topological arrays of one, two, three (or more) dimensions, as in the tone .scale; the color pyramid, the prism of odors, etc. Moreover, there are cases of remarkable intersubjective agreement even in purely introspective judgments of the wetiical relations of given qualities or intensities with each other. S. S. Stevens,1 for example, found by careful experimentation that subjects agreed on what was the mid-point in a series of sounds of varying intensities. Shapes, sizes, distances, durations -- all-as-directly-experienced are often susceptible to metrical estimates far surpassing in accuracy anything the uninformed might ever expect.
As regards the differences among such experiential modalities as colors, sounds, and smells, or between larger classes such as the sense qualities and the emotions, it must of course be recognized that they differ qualitatively from one another; and no merely quantitative distinction will serve as a criterion to characterize their different generic features. Dualists have tried to utilize this as an argument by asking, Why should there be more than one basic quality (or modality, for the matter of that), if all of the manifold phenomenal data are to be nothing but the subjective aspects of basically homogeneous brain processes? But the answer may well be that there are sufficient topographical, configurational, and quantitative differences even among those "homogeneous" neural processes.
(b) The magnitudes determined by physical measurement, and syntactically represented in scientific language by functors,2 differ among themselves in a way that can hardly be called anything but "qualitative". What else can we say about the differences between, e.g., mass, temperature, pressure, electric current intensity, electromotoric force, gravitational field intensity, etc.? What is it that is, respectively, indicated by thermometers, manometers, ammeters, voltmeters, etc.? I think it is entirely justifiable to speak of these scientific variables as qualitatively different. To be sure, they are not directly experienced qualities. But is there any good reason for restricting the term "quality" to the phenomenally given?
I conclude that the attempt to define "mental" and "physical" in terms of the distinction qualitative-quantitative begs the question. It makes perfectly good sense to speak of mental quantities and of physical qualities.
Notes 1. Cf. his article in the Handbook of Experimental Psychology (S. S. Stevens, ed.). New York: Wiley, 1951.
2. Cf. Carnap (65, 68); Reichenbach (274).