The concept of the additivity of molecular polarizabilities has been shown to provide a powerful means of rationalizing experimental measurements of the dielectric constants of oxides and of recognizing anomalous data. It is pointed out that the deviant behaviour of MgAl₂O₄ spinel at room temperature is readily accounted for by an imbalance in the anti-ferroelectric arrangement of permanent dipole moments which arise naturally from its crystal structure. At higher temperatures the dipole moment per octahedral site, calculated to be 7.56*10^-31 C m, may give rise to a much larger dielectric effect if these dipoles arise through a mechanism similar to that operating in the isomorph MnFe₂O₄.