Harmony Explained: Progress Towards a Scientific Theory of Music (2014)
I came up with something of a theory of rhythm. I don&#x27;t know anything about music theory, so, for all I know, the theory is not new or a better theory already exists. But it&#x27;s simple, so I&#x27;ll share the main idea.<p>I think that rhythms are perceived like echos. So, in 4&#x2F;4 time with beats on quarter notes, beat #2 is an echo of beat #1 (the main beat), beat #3 is an echo of beat #2, and beat #4 is an echo of beat #3. Then, the main beat sounds again and the whole thing repeats.<p>Now, if that makes sense, you can forget about echos. What matters is that there is a chain of causation. The listener perceives that Beat #1 causes beat #2, which causes beat #3, and so on. The listener unconsciously creats a theory of causation that explains the rhythm.<p>Now set aside music for a second. Imagine that you hear a sequence of sounds:<p><pre><code>  1. &quot;Oops!&quot;
  2. (Crash!)
  3. (Baby crying)
</code></pre>
Since they occur together, they are perceived as being causally related. Now, back to music. Within each repeating unit (usually a measure), the listener always has a working theory of causation to explain the rhythm. The theory has the form of a tree, with child nodes caused by the parent node.<p>When rhythms mutate over time, the change will sound small if the change only affects a leaf. The change will sound bigger if the change affects a complete branch. And, the change will sound jarring if it violates the theory of causation, i.e. by removing the cause without removing the effect.<p>Multiple rhythms can be superposed over each other, so the theory of causation can be a tree with multiple branches. For ex.:<p><pre><code>  Main beat -&gt; rhythm1
    AND ALSO
  Main beat -&gt; rhythm2.
</code></pre>
If rhythm2 is added to rhythm1 after rhythm1 has been playing already, rhythm2 is perceived as a distinct chain, which is caused by the main beat. Hence, rhythm2 can be removed as a unit without violating causation.