The song is set in common time. Houston's verse is written in the key of B minor and features a basic chord progression of A-G1, and the song modulates to D major for her chorus. Her vocals in the song range from the note of F3 to F5. Carey's verse is set in the same key, but the song changes to E major for her chorus. Her vocal range in the song spans from the low note of E3 to the high note of A5, spanning more octaves than Houston's voice in the song. The song's key changes again in the last chorus, to F-sharp major. Steve Jones from "USA Today" called the song a "soaring duet" and felt that the song would be able to appeal to many types of listeners and "cross all genres."