more open-ended tag: as "thinking man's metal"; however, this tag refers to the intellectual elements behind the music, as opposed to exclusively aural ones. Due to the difficulty in pigeonholing, some fans and critics label Isis as post-metal. This genre is accepted to contain similar-sounding contemporaries such as Pelican, Cult of Luna and Callisto; however, Isis are often credited with the formulation of the genre with the release of Oceanic. In addition to the aforementioned post-metal, hardcore punk, and doom metal, some have described Isis as sludge metal, progressive metal, and even metalcore. Isis did not write their music for mainstream appeal according to guitarist Michael Gallagher: "... we've never tried to be on the radio, and we've never tried to please others. We've simply done whatever we've wanted to do, and we've all decided to be happy with the results." Equipment Circa 2005, both Turner and Gallagher used Gibson Les Paul guitars with Mesa Boogie V-Twin preamp and a Mackie power amp. Conceptual elements Turner has gone on record saying "I like the idea of preserving at least a little shred of mystery and making the band to be more an entity—without hopefully sounding too pretentious – as a work of art [than a traditional rock band]". Turner has also said in an interview in New Zealand music magazine Rip It Up that "we don't want to hand-feed everything to the listener. We just want to have a sense of mystery". There is a definite attitude that art and music are interchangeable and synonymous to the band; he feels that "the songwriting and the artwork come from the same place". This logic relates to visual and aural aspects as well as overt intellectualisation, through literary references and driving philosophies. Books such as Don Quixote, House of Leaves, Labyrinths and the philosophies of Jeremy Bentham have all played a role in shaping the themes of Isis' releases. There is an overt intention of progressing heavy music present in Isis' output; a desire to further the intellectual cause that pushes them forward. This is evident within the clear progression of their sound from release to release, their influence on heavy music, and their acceptance in art circles where other metal bands are not so readily embraced. Their stated goal is "not to break away from the scene that [they] came from, but to expand upon it". Publications such as Terrorizer attest