In the Absence of Truth is the fourth full-length studio album by American post-metal band ISIS, released by Ipecac Recordings on October 31, 2006.

[3] The album expands upon the group's previous full-length, Panopticon, further exploring lead singer Aaron Turner's clean vocals (though his former techniques, which relied more on screaming and growling, are still present as well).

"[11] Drummer Aaron Harris explains this further, saying that the album is based “on personal perception of anything [...] and what's true and what's not true.”[12] Gitta Sereny's book on Nazi Minister of Arms, Albert Speer, also inspired Turner; to him, it illustrated how society has a “tendency to portray the enemy as very one-sided and one-dimensional.”[13] The album takes its title from a quote often attributed to Hassan-i-Sabbah: "Nothing is true, everything is permitted".

"[11] Track titles explicitly reference Hassan-i-Sabah's garden Firdous e Bareen, and Dulcinea, a character in Don Quixote.

In celebration of Isis' tenth anniversary,[17] the tracks "Holy Tears" and "Not in Rivers, but in Drops" were each released in single format in February and October 2008, respectively.

Stylus Magazine repeated similar sentiments as those of the previous reviews, but did not feel that re-using a successful formula was a burden, Cosmo Lee saying "it's not Isis' fault that they sound unoriginal these days.

[33] Writing for Alternative Press, Aaron Burgess states that "save for the brief distorted squalls of "Garden of Light" and the pummeling metallic grooves of "Not in Rivers, But in Drops," there's barely anything keeping Isis tethered to the rigid "post-metal" genre they helped inspire".

In the Absence of Truth takes them into its dark heart squalling, whispering, crawling, drunkenly falling into its center, punching, screaming, and kicking until there is nothing left but silence.

[29] Brandon Stosuy of Pitchfork Media posits that "the set's so finely wound that on the first few listens it seemed like the steady diet of Tool had perhaps transformed Isis into an emaciated, innocuous version of their older selves".

[24] Tracks selected as stand-outs include "Not in Rivers, but in Drops",[34] "Garden of Light",[1] and "Dulcinea", specifically praising the climax of the piece.

[32] "Holy Tears" is labeled as revealing the "true, outward strength of Isis",[35] and is selected as "a beacon of light in the darkness" in an otherwise scathing Delusions of Adequacy review.