  Let $X$ be a proper, geodesically complete CAT(0) space which satisfies Chen
and Eberlein's duality condition. We show the existence of a strong notion of
rank for $X$ by proving that the parallel sets $P_v$ of geodesics $v$ in $X$
are generically flat. More precisely, let $GX$ be the space of parametrized
unit-speed geodesics in $X$. There is a unique $k$ and a dense $G_\delta$ set
$\mathcal{A}$ in $GX$ such that $P_v$ is isometric to flat Euclidean space
$\mathbb{R}^k$, for all $v \in \mathcal{A}$. It follows that $\mathbb{R}^k$
isometrically embeds in $P_v$ for every $v \in GX$.
