Definition
A tangled hierarchy is a hierarchy in which the supposedly higher level influences the supposedly lower level, in a closed loop that makes the level structure circular rather than strictly stratified. The term comes from Douglas Hofstadter's Gödel, Escher, Bach (1979). In an ordinary hierarchy, influence runs in one direction — atoms compose molecules compose cells compose tissues compose organs. In a tangled hierarchy, influence also runs the other way: the higher level reaches back down and modifies the lower level that constitutes it.
Tangled hierarchies are the architectural prerequisite for strange loops. Wherever influence runs both up and down between levels, fixed-point-like phenomena (self-reference, self-replication, consciousness on Hofstadter's account) become structurally possible.
Why it matters
How it works
A tangled hierarchy needs three pieces. First, multiple levels with distinct vocabularies — neurons vs symbols, atoms vs molecules, branches of government vs individual legislators. Second, downward causation: high-level patterns must be able to constrain or modify lower-level events. (The self-symbol modulating which neurons fire; the legislature passing a law that constrains executive behavior; an organism's developmental program switching gene expression.) Third, upward emergence that re-produces the high-level pattern from the modified low-level events, closing the loop.
The result is a system in which no single level is fundamental. Each level supports and is supported by the others, and questions about the "real" level — is the law the words on paper, the courts' interpretation, or the executive's enforcement? — have no single correct answer.