Thick as a Brick was viewed by some critics as Jethro Tull's first progressive rock album,[REF] contrasting with the group's earlier work.
The album prominently features flute, acoustic and electric guitars and Hammond organ, which had been used previously,[REF] but the instrumentation includes harpsichord, xylophone, timpani, violin, lute, trumpet, saxophone, and a string section-all uncommon in the band's earlier blues-inspired rock.