We theoretically demonstrate the coherent control of the effective susceptibility of a duplicated two-level system. The control is obtained for a linearly polarized weak field in the presence of a much stronger orthogonally polarized field. For small optical depths, the effective susceptibility chi(eff) behaves as chi(lin)e(2i phi) (chi(lin) is the linear susceptibility, phi the phase shift) allowing coherent control of the optical response. For large optical depths, chi(eff)approximate to chi(*)(lin), turning an absorber into an amplifier without affecting the dispersion.