As a led-up to tomorrow's planned (and unusual) book-review, I offer you live versions of the first Chicago song to stick in my mind. It is the first song on the first album, and was never a top-40 hitbound single. Written by the late, great Terry Kath, it is called Introduction.
The first version is the earliest. It is audio-only, very high-quality, and comes a 1969 performance at the Filmore West, two years after the band's formation and the year their first album ("Chicago Transit Authority") was released. It is the first song on that album.
The next is a not very high-quality (but still fun) video of a live performance in Japan from 1972. All the original members are seen, and I'm assuming nothing's offensive in the captions.
Finally, fast-forward well over three decades, and you see original Chicago drummer Danny Seraphine performing the same song (sans horns) with his new band California Transit Authority.
"Why," you ask, "is Danny doing the song with a different band now?" The answer is in tomorrow's planned book-review.