  Blend lines form an integral part of the theoretical analysis and modeling of
the polarized spectrum of the Sun. Their interaction with other spectral lines
needs to be explored and understood before we can properly use the main
spectral lines to diagnose the Sun. They are known to cause a decrease in the
polarization in the wings of the main line on which they superpose, or in the
polarization of the continuum, when they are assumed to be formed either under
the local thermodynamic equilibrium (LTE) conditions, or when their intrinsic
polarizability factor is zero. In this paper, we describe the theoretical
framework to include the blend lines formed under non-LTE conditions, in the
radiative transfer equation, and the numerical techniques to solve it. The
properties of a blend line having an intrinsic polarization of its own and its
interaction with the main line are discussed. The results of our analysis show
that the influence of the blend lines on the main spectral lines, though small
in the present context, is important and needs to be considered when
interpreting the polarized spectral lines in the second solar spectrum.
