In this work, we prove that the ratio of torsion and curvature of any dual rectifying curve is
a non-constant linear function of its dual arc length parameter. Thereafter, a dual dierential equation
of third order is constructed for every dual curve. Then, several well-known characterizations of dual
spherical, normal and rectifying curves are consequences of this dierential equation. Finally, we
prove a simple new characterization of dual spherical curves in terms of the Darboux vector.