We present the results of a theoretical study for the interpretation of the optical and magneto-optical spectra of PrSb. In particular, we address the question of the assignment of the unexpectedly low optical and magneto-optical signals to the ${\mathit{f}}^{2}$\ensuremath{\rightarrow}${\mathit{f}}^{1}$d transition. We use two different approaches: the crystal-field approach, suitable for the Pr 4f states assumed to be localized, and the band approach for the conduction electrons polarized by the 4f states. The two pictures are merged by the technique of a fixed 4f spin moment used to perform the spin-polarized calculations for the conduction electrons. We calculate the 4f spin moment ${\mathrm{\ensuremath{\mu}}}_{4\mathit{f}}^{\mathit{s}}$ in the crystal-field ground state of ${\mathrm{Pr}}^{3+}$ including the molecular-field correction \ensuremath{\lambda}M. From the local spin density approximation calculations we evaluate the molecular-field constant \ensuremath{\lambda}, which agrees with the previous value, the interband conductivity, reflectivity, and the Kerr rotation angle for the conduction electrons. On the basis of our model we find that the weak intensity of the optical and magneto-optical signal is ascribable essentially to electric dipole selection rules among crystal-field states. Finally, we interpret the structure at \ensuremath{\simeq}1 eV in the off-diagonal conductivity spectrum in terms of the ${\mathit{f}}^{2}$\ensuremath{\rightarrow}${\mathit{f}}^{1}$d transition. This is in agreement with two different reflectivity spectra.