Excerpt: “Music and Dance” from Kadavy’s Design Hackers

As many of you know, I am a full-stack web developer by profession. As part of our weekly reading hour, I read (and was clearly excited by) the following passage from David Kadavy‘s Design <for> Hackers:

Music and Dance

Although some experimentation has been done with irrational numbers, such as the golden ratio, the most popular music tends to contain very simple patterns. Most rock songs are in 4/4 time, meaning that there are four beats per measure. Also occasionally found in popular music is 3/4 time, meaning there are three beats per measure; 3/4 time is the time signature of waltz music.

One of the most fascinating examples of proportion in music can be found in proportion’s influence on tone, as shown in Figure 5-15. If you strum an open guitar string tuned to C, you’ll hear a C note. If you shorten the length of the string to half its original length, you’ll hear another C note, but this time an octave higher (the eighth note in the major scale). If you take that same string and strum it instead at three-fourths its original length, you’ll hear an F note (the fourth or subdominant note in the major scale). If you strum the string at two-thirds its original length, you’ll hear a G note (the fifth or dominant note in the major scale).

Figure 5-15 from Design for Hackers by David Kadavy

Figure 5-15

Shortening a guitar string to three-fourths or two-thirds its original length produces the subdominant and dominant notes, respectively, in the major scale.


By forming chords from these root notes – C, F, and G – you have a common blues chord progression, and the most common chord progression in rock and pop music, properly referred to as “I–IV–V” (for the roman numerals for 1, 4, and 5). Pull this chord progression from the D major scale (D, G, A), and you have the chord progression of “Twist and Shout” as sung by the Beatles.

Dance, naturally, is the bodily expression of music. Salsa dancing consists mostly of 3/4 proportions. As shown in Figure 5-16 (top), the lead steps forward and then back within the span of three beats, and then pauses for the fourth beat. The lead then repeats the process, this time stepping backward. The pause on the fourth beat gives an exciting sense of inertia for turns and spins.

Bachata is another form of Latin dance. It originated in the Dominican Republic and breaks up steps along the proportions of 3/4. The leads steps sideways for three beats, taps his trailing foot on the fourth beat, and then repeats the process in the other direction (see Figure 5-16, bottom).

Figure 5-16 from Design for Hackers by David Kadavy

Figure 5-16

The Latin dances of salsa (top) and bachata (bottom) both consist of steps that involve three beats of motion and one beat of pause, before changing direction.


(p. 122-123)

Works Cited

Kadavy, D. (2011). Design for hackers: Reverse-engineering beauty. Chichester: John Wiley & Sons.

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