3) The high chemical versatility of phosphorus in phosphosulfides implies that direct-gap, low-effectivemass semiconductors can be generated by completely different combinations of frontier orbitals. Ag 3 PS 4 and Ba 4 P 2 S illustrate this concept. This is a unique design handle for phosphosulfides, and it could be exploited to engineer defect tolerance by engineering the orbital character of the bands. 4) Phosphosulfides are a vast material space, because of the wide allowed range of phosphorus oxidation states. We estimate that the number of chemically plausible phosphosulfides exceeds the corresponding number of oxysulfides by almost an order of magnitude. 5) Phosphorus-rich phosphosulfides (i.e., those with P/S > 1) have never been synthesized. Nevertheless, the few ones that have been computationally studied appear to be thermodynamically stable and with optimal optoelectronic features. 6) Quaternary phosphosulfides are often thermodynamically stable, and there are concrete examples of quaternaries with improved optoelectronic properties with respect to their ternary constituents. KAg 2 PS 4 is an illustrative case.