[link to original on tumblr]
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While they're in different tempi, the rhythms are the same (I think I've notated them correctly):
Aside from the key, the notes that comprise the parts are the same degree on the scale. It's the 5th, the 7th, and the octave (the root).
"Whenever You're Ready" is in C major, so it's G (the 5th), B (the 7th), and C (the octave). "Time of the Season" is in E minor, so it's B (the 5th), D (the 7th), and E (the octave).
I should note that these aren't the same intervals. The interval between the 7th and the octave is a half-step in a major scale but a whole-step in a minor scale. So you couldn't transpose the opening bass part for "Whenever You're Ready" up a few steps and get the opening bass part for "Time of the Season," but they are incredibly similar. For instance, the classic clap and exhale from "Time of the Season" fits during the opening of "Whenever You're Ready."
After I realized this, I thought it really interesting just because it seems to be such a feature of Argent's writing (that rhythm in "Time of the Season" is a fairly frequent topic in interviews), but then I remembered the story about "Hold Your Head Up" and how Chris White wrote it from a riff Argent (the band) improvised when playing "Time of the Season." It seems that in concerts Rod Argent often introduces "Hold Your Head Up" with that story. But because that phrase in the bass parts for "Whenever You're Ready" and "Time of the Season" are essentially the same, that story could have an even broader scope.