It is generally accepted that certain intervals in music sound "harmonious", i.e. 3rds, 4ths and 5ths. Why is this so? Why do these certain intervals constitute a pleasant sounding harmony, as opposed to jarring, dissonant intervals like 2nds and 7ths? I do not believe it is a matter of taste - most people, even those with no musical training will uniformly identify a harmony as harmonious (or in tune) or dissonant (or out of tune, I suppose). However, I am open to being disproved on this point.

It's an intriguing phenomenon. And it turns out, so I gather, that it's not confined to humans. Various animals differ in their responses to what we label consonant and dissonant intervals. Why this should be isn't something that a philosopher, as such, is in a good position to say. It clearly has some physiological basis and seems to have something to do with the phenomenon of "beats" (something you can actually experience as pulses when two high-pitched notes that differ slightly in pitch are played together.) One study I discovered (by Jonatan Fishman et al. of Albert Einstein medical college) looks at the neural correlates of dissonance in macaques and in humans. If you're able to follow the neurophysiological details (I'm not) you can have a look at the link. There are also references to earlier work.

There are still some things left over that a philosopher might want to puzzle about. One is the sort of thing that physiology might straightfowardly help us understand: why is it that intervals we identify as dissonant are also perceived as unpleasant when we hear them in isolation? Another is famously hard to get a handle on: suppose that Fishman and his colleagues are right and that perception of dissonance has to do with "oscillatory neuronal ensemble responses phase-locked to the amplitude-modulated temporal envelope of complex sounds" -- whatever exactly that means. How do we get from that to "what it's like" to experience dissonance? Of course, that's of a piece with a much more general question: how do we get from physiological accounts of perception and sensation to the way that we experience things? This is a question that divides philosophers deeply; they are nowhere near agreeing on what would count as an answer, nor even on whether the question is a good one to begin with.

Fishman et al point out that there's a distinction we need to keep in mind: the dissonance of intervals (such as the minor 2nd or the augmented 4th) vs. musical dissonance and consonance. Dissonant intervals occur all the time in music that we find quite pleasing (as I'm sure you're already more than well aware.) And it's not just that the alternation between dissonant and consonant chords adds musical interest; whereas a major 7th (e.g, C-B) sounds dissonant by itself, when we add notes to form a major 7th chord (as in C-E-G-B) the result sounds pleasant to most people, even in isolation. One suspects that there's a complex combination of cultural and physiological factors at work here; this is clearly an area for fruitful collaboration among aestheticians, psychologists and physiologists.

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