If artists have their whole lives to write their first album, and a year to write their second, their third usually represents a coming to terms with their successes, failures and expectations. But what about fourth albums? If an artist makes it that far, are they obligated to steer new courses or hold steady? On our Top 10 Fourth Albums, it's a little of both, with some of classic rock's biggest names settling into styles while solidifying their sounds ... and turning out their most defining works as a result.