From The Art and Popular Culture Encyclopedia
Soft rock, also referred to as light rock or easy rock, is a style of music which uses the techniques of rock and roll to compose a softer, supposedly more ear-pleasing sound for listening, often at work or when driving. Soft rock is usually sung with higher-pitched vocals, and the lyrics tend to be non-confrontational, focusing in very general language on themes like love, everyday life and relationships. The genre tends to make heavy use of pianos, synthesizers and sometimes saxophones. On some occasions soft rock may include electric guitars. Or, as shown in the Bee Gees, soft rock can also include acoustic guitars. Twelve string guitars may also be used in soft rock.
Soft rock as a specifically to a style of rock that emerged in the early 1970s, both as a reaction against the increasingly heavy music (hard rock and heavy metal etc.) that dominated rock at the time, and also as a reflection of the changing priorities of the Baby Boom in the early 1970s. What set 1970s soft rock apart from its 1960s counterpart, which for lack of a better word is usually just called "pop", is that in the 1960s pop existed for those who simply didn't like rock; the 1960s' pop artists usually were vocalists who were stylistic throwbacks to the pre-rock era. Soft rock developed organically to suit the needs of those who did have rock listening experience; as such, it can be considered a bona fide rock genre.
Soft rock became hugely popular later in that decade. By 1977, some radio stations, like New York's WTFM and WYNY, had switched to an all-soft-rock format. Around that same time, Chicago, which had previously been a jazz-rock band, switched to soft rock and reached their biggest commercial successes. British/American blues band Fleetwood Mac achieved its greatest success after adopting this genre. Their success was further solidified after they had the highest selling soft rock album ever, Rumours. Even Led Zeppelin, considered by some to be standard bearers of hard rock, flirted with the genre at the time in songs like 1979's "All My Love". By the 1980s, tastes had changed and radio formats reflected this change; the genre evolved into what came to be known as "adult contemporary", a pop categorization that bore less overt rock influence than its forebearer.