[colanderman]

He doesn't go nearly enough into depth to say anything surprising. That "C/Am" is by far the most common is not surprising at all; C major is the first key any music student learns.

I wish he separated out the major keys from minor keys. It's easy to tell the difference; almost no-one writes pop music in the natural minor (which shares a key signature with the relative major), as it has no dominant fifth. Rather, melodic and harmonic minor keys are used, which have a distinct key signature from major keys (both have the 7th note of the scale raised to accommodate a dominant fifth chord). This should make them easy to detect.

The "Chord Use" chart also does not say much; C, F, and G are the I, IV, and V chords of the key of C major (the Roman numerals indicating their relative position in the scale), which together form the basic pop progression. Much more useful would have been to bin the chords relative to the key in which the song is written, rather than as their absolute pitch.

What I would also like to see is a histogram of chord progressions, e.g. I-IV-V vs. I-IV-ii-V vs. I-vi-VI-V etc. His preview of next week hints at this, but again he should use relative chord names rather than absolute chord names.

The preview graph, "Chords following em", is not very surprising either. Since this is an absolute chart rather than a relative one, we must assume that the data is reflective of the chord's use in the most common key (C). (Em will rarely occur in a song written in Am; rather, it will be altered to an E7 dominant chord.) Of the other chords available in the key of C, C and G both share two out of three notes with Em and thus are unlikely to be used due to lack of motion between them. Bdim is rarely used in C.

This leaves Dm, F, and Am as likely to occur following an Em. The E and B notes of the Em chord are a half-step below the next higher note in the scale, so they will tend toward upward motion, meaning the next chord will likely contain an F or a C. F contains both of these, hence its prominence in the graph. Both Am and Dm contain one of these notes; however Em->Am is an upward (downward) skip of a fourth (fifth), which is a resolving motion – it is likely that the next few chords following these two will be Dm, G, and C, to continue this motion. Em->Dm, being a skip of a second, does not share this property and hence should not be as common.

[msluyter]

I was going to write up pretty much the same analysis of the Em->X progression. I think you aptly covered it. Interestingly, though, as you say Em->C sounds relatively static, I bet you see a lot more C->Em than the reverse (which should suffer from the same problem), and I'm hard pressed to say why exactly.

[colanderman]

My guess would be that it's a precursor to an Em->F or Em->Am transition; i.e., if you wanted to transition to a minor mode convincingly from C, you'd toss the Em (or even E7) in there before hitting Am. Example: Santeria by Sublime (I-III-vi-V)

[Goladus]

I can't speak for pop music, but you can move from Em to C/E to F, which is basically a delayed resolution of the E to F, but the C Major is definitely there.

[cnanders]

Regarding "chords following em": Since all of the songs were transposed to the key of C, em == iii, am == vi, and F == IV. Really what the post says is IV and vi follow iii most often in popular songs.