Radices arose naturally in previous efforts to classify normal subgrou
ps of SL(2, A) and Sp(4, A), A a commutative ring. They appeared as su
bstructures of A and the matrix algebra M-2(A), respectively, associat
ed with normal subgroups, and defined by some seemingly ad hoc closure
properties. In this paper we give an abstract, axiomatic definition o
f radices, which should be the correct definition in any context to wh
ich the axioms apply.