In the 1960s, the study found, romance dominated - as you might expect - though a whiff of rebellion crept in as it developed into the decade with a conscience. In the darker 1970s, people were still singing about love, but from a more jaded perspective: loss and break-ups loomed large.
That development continued into the 1980s - when aspiration also became a common theme - and by the 1990s, "love" was no longer the most-used word. In the 2000s, it didn't even make the top eight (while "nigga" did).