  The PSR embodies the position that everything is explainable and thus intelligible. The PSR can also be used to explain a number of different things, including the coherence of a thing's essence, that essences have a cause, and the existence of things. These points can also be captured by the depiction of the PSR as the principle which accounts both for the possibility of things (i.e. due to the coherence of their essences), and for the actualization of essences (i.e. there is a cause of their actualization which thus brings them into existence). Sometimes the PSR is taken to have a very wide domain (e.g. all truths and all events), while sometimes the PSR is taken to have a narrower domain. For example, the domain of the PSR is sometimes only events, but not truths, even while some truths (but not mathematical truths) can be translated into events. Or, as another example, sometimes the domain of the PSR is taken to be only the domain of contingent truths but not necessary truths. Sometimes the domain of the PSR is taken to be all truths, with the sufficient reason for the truth of necessary truths being that their negation violates the PC. There are different ways of thinking of the relation between the PC and the PSR, the two most prominent being, first, that the PC and the PSR are equally fundamental, and, second, that only the PC is fundamental, with the PSR either playing a role of secondary importance or being derived from or proven by the PC. Finally, as with the PC, the PSR can operate in different realms. For example, it can operate in the realm of modality, perhaps serving to explain contingent truths. Alternatively, it can operate in the realm of standard areas of human inquiry, perhaps serving as the foundation of metaphysics, natural theology, physics, and many other disciplines (but not mathematics).