Reasoning of the court

The district court had made the dacision based on the music behind the lyrics and title. Since song names cannot be copyrighted it was seen that since the only thing that was in direct relation to the original was the bass line and the district court stated that 2 Live Crew had not “helped themselves overmuch.” 754 F. Supp., at 1156-1157

The court of appeals disagreed, stating that "while it may not be inappropriate to find that no more was taken than necessary, the copying was qualitatively substantial. . . . We conclude that taking the heart of the original and making it the heart of a new work was to purloin a substantial portion of the essence of the original." 972 F.2d, at 1438.”
http://www.bc.edu/bc_org/avp/cas/comm/free_speech/campbell.html