Bill Crow now and then allows me to borrow an anecdote from his Band Room column in Allegro, the monthly publication of New York Local 802 of the American Federation of Musicians. Here’s an item from his December column.
When Gerry Mulligan formed a quartet in Los Angeles and hired Chet Baker on trumpet, the musical chemistry between them produced some wonderful results. One night Dick Bock visited the Haig, the club where they were playing, and asked Gerry if he could sell him a record. Gerry told Bock that the group hadn’t recorded yet, and Bock said, “Well, how much does it cost to make a record?” When he found out that it could be done for just a few hundred dollars, he got the quartet into a recording studio, and the Pacific Jazz label was born. It went on to successfully record many West Coast jazz groups.
The Mulligan Quartet records were an immediate hit. Everyone was amazed at the interplay between the two horns, and the inventiveness of their soloing. Someone remarked to Gerry, “I understand that Chet doesn’t know anything about harmony.” Gerry replied, “He knows everything about harmony! He just doesn’t know the names of the chords.”
Here’s evidence to support Mulligan’s answer about Chet’s harmonic knowledge.