Glasses of composition (in equivalent percent) (28 -x)Mg:xY:56Si:16Al:(100 - y)O:yN, with x = 0, 14, or 28 for y = 0 and 15 and with x = 0, 7, 14, 21, or 28 for y = 10, were prepared by melting and casting. For glasses where the nitrogen content was varied for a constant cationic ratio, the glass molar volume (MV), compactness (C), Young's modulus (E), glass-transition - temperature (T-g), and dilatometric-softening temperature (T-ds) varied linearly as the nitrogen content increased, with MV decreasing and the other properties increasing. From the incremental changes in these properties with nitrogen content, for glasses with x = 0, 14, and 28, good linear fits (R-2 > 0.99) were obtained, and best-fit slopes are reported here. The property changes and their linearity were consistent with the increased cross-linking of the glass network by tricoordinated nitrogen. The replacement of magnesium by yttrium led to a nonlinear decrease in glass compactness and to nonlinear increases in MV, T-g, and T-ds. However, linear correlations were found for MV and ionic volume and for T-g, T-ds, and the coordination of (Si,Al)(O,N) tetrahedra of the glass structural units to the modifier cations not involved in charge compensating aluminum ions in fourfold coordination. The replacement of magnesium by yttrium had little effect on Young's modulus, and this result was related to similar changes in the compactness, C. The present results showed that the effects of substituting nitrogen for oxygen and yttrium for magnesium are independent and additive; thus, no synergistic effects of anion and cation substitutions were observed.