Given that her "hypothesis" about music appears no better or worse than any of her other theories, it is difficult to explain why she would consider it a mere hypothesis. Rand's theories of concepts and value are also mere hypotheses. Her attempts to "prove" or "validate" them are no more convincing than her hypothesis about music. So why did she recognize the hypothetical character of her theory of music while ignoring the fact that the rest of her philosophy was also hypothetical?
Oddly enough, her theory of music at least attempts to make use of scientific evidence (which cannot be said of most of her other theories). To be sure, the scientific evidence she references is very old: namely, Helmholtz's 1863 Die Lehre von den Tonempfindungen als physiologische Grundlage für die Theorie der Musik (On the Sensations of Tone as a Physiological Basis for the Theory of Music),
She presents her hypothesis as follows:
From the standpoint of psycho-epistemology, I can offer a hypothesis on the nature of man’s response to music, but I urge the reader to remember that it is only a hypothesis . . .Even as a hypothesis, this is pretty wretched stuff. It is not even consistent with Rand's own pronouncements about music.
One may listen to noise for an hour, a day or a year, and it remains just noise. But musical tones heard in a certain kind of succession produce a different result—the human ear and brain integrate them into a new cognitive experience, into what may be called an auditory entity: a melody. The integration is a physiological process; it is performed unconsciously and automatically. Man is aware of the process only by means of its results.
Helmholtz has demonstrated that the essence of musical perception is mathematical: the consonance or dissonance of harmonies depends on the ratios of the frequencies of their tones. The brain can integrate a ratio of one to two, for instance, but not of eight to nine. . .
The psycho-epistemological meaning of a given composition lies in the kind of work it demands of a listener’s ear and brain.
A composition may demand the active alertness needed to resolve complex mathematical relationships—or it may deaden the brain by means of monotonous simplicity. It may demand a process of building an integrated sum—or it may break up the process of integration into an arbitrary series of random bits—or it may obliterate the process by a jumble of sounds mathematically-physiologically impossible to integrate, and thus turn into noise.
The listener becomes aware of this process in the form of a sense of efficacy, or of strain, or of boredom, or of frustration. His reaction is determined by his psycho-epistemological sense of life—i.e., by the level of cognitive functioning on which he feels at home.
According to Rand's hypothesis, the "psycho-epistemological sense of life" evoked by music depends on the ability to resolve the complex mathematical relationships of musical tones. What this suggests is, first of all, that musical response depends on the level of an individual's cognitive functioning. Since cognitive functionality presumably differs from one individual to another, this means that musical values are relative, rather than objective (i.e., they are relative to the individual's level of cognitive functioning). Although Rand does not explain how music conveys either a benevolent or malevolent sense of life, the unstated implication is that it has something to do with the ability to resolve complex mathematical relationships and to the process of building an integrated sum. This would suggest that an individual with a benevolent sense of life would respond to music which, given his level of cognitive functioning, demanded his full capacity at resolving complex mathematical relationships and building integrated sums. In other words, music which he would perceive as having a benevolent sense of life would be just the sort of music that most he found most challenging to process and resolve. This ability would differ from person to person. An individual with a low level of cognitive functioning might find a popular song challenging and therefore "benevolent." The same individual would, however, be frustrated in his attempt process and resolve a Beethoven string quartet, which he would therefore regard as "malevolent." A person with a higher level of cognitive functioning, on the other hand, would find the popular song boring, and therefore "malevolent," but the Beethoven quartet challenging and therefore "benevolent."
As Rand was never very good at ferreting out the more problematic implications of her theories, she failed to notice these implications in her hypothesis about music. If she had noticed them, it's hard to believe that she would have presented this theory, even if only as hypothesis. In any case, it should be obvious that this hypothesis is not consistent with her own aesthetic judgments about music. Rand believed (although she could not prove) that Sergei Rachmaninoff was "objectively" the greatest of composers. If, however, one's response to music depends on one's the level of cognitive functioning, than the objectivity of musical values, as I have already noted, is no longer warranted. Even relative to a specific level of cognitive functioning, Rand's judgment is problematic. After all, is Rachmaninoff any more complex than Arensky, Cui, Balakirev, Medtner, Miakovsky, and any number of composers who wrote in a similar style, yet who are generally regarded as his inferior? Since the complexity of many of the works of these composers is about on par with Rachmaninoff's best works, there doesn't seem to be any reason to prefer one over the others. Rand's hypothesis doesn't actually provide a basis for musical values or judgments about music. So even as a hypothesis, it's a complete failure.
There is further problem with Rand's hypothesis. What on earth does Rand mean by the phrase "mathematically-physiologically impossible to integrate." Presumably, she is referring to "dissonant" modern music, particularly the atonal music of Schoenberg and the high modernists. However, it should be noted that nearly all serious music contains dissonances (i.e., chords that are "mathematically-physiologically impossible to integrate"), and that Rand's implied criticism of modern music could be applied to classical music en toto. Dissonances are essential in developing drama, tension, and resolution in serious music. Such dissonances are resolved, not by integrating their notes (which is, after all, "physiologically impossible"), but by juxtaposing them with consonant chords. Moreover, there is absolutely no evidence to support the notion that listening to physiologically unresolvable chords or melodies necessarily leads to frustration or boredom, as is suggested in Rand's hypothesis. Experiments have demonstrated that prolonged exposure to atonal music develops the ability to listen to music without expecting harmonic resolution.