Hi V4E. It was a lecture at Wesleyan University in Middletown, CT. He had beein in their music dept for years. He may still have been at the time. The "lecture" consisted of reading rambling notes on several subjects like the environment, civil rights, brotherhood. I don't recall anything about music, but there may have been while I was nodding. Cage was described by some colleagues as a very generous ("give you the shirt off his back" was used) and helpful person.
He was a pioneer in "prepared piano" and chance music. The I Ching is mentioned in connection with chance. His most notorious work is the "silent sonata". It's a 3-movement work of silence for 4 min 23 sec. It was once "performed" by David Tudor, who approached the piano and closed the keyboard, thus beginning the first movement. When he opened the keyboard the movement was concluded. The other 2 movements began and ended the same way. This description was once reported in Time Magazine, which is where I read it. The "music" is supposed to be the ambient sounds (traffic, coughing, foot-shuffling, etc). It could be considered an example of chance music, although there are usually musical sounds involved in chance.
Robert J Lurtsema had a program emanating from WGBH in Boston for many years. It was called Morning Pro Musica. One time he interviewed Cage. Lurtsema said something that prompted Cage to say "I'm not a composer at all". Lurtsema seemed not to know how to take that. I thought it was an accurate claim. Stravinsky had once claimed not to be a composer, but rather an inventor of music. Cage claimed no connection with music at all. Considering that the word "music" has a relatively constant meaning to most people, Cage was really apart from that meaning. I once heard a nornal sounding ballet by Cage (I think it was called The Seasons, about a half hour long), so he was a traditional composer at one time in his life.
Well, that's about all I can say about Cage, other than I can leave him or leave him, "musically".