Brute fact
In contemporary philosophy, a brute fact is a fact that has no explanation. More narrowly, brute facts may instead be defined as those facts which cannot be explained (as opposed to simply having no explanation). To reject the existence of brute facts is to think that everything can be explained. ("Everything can be explained" is sometimes called the principle of sufficient reason). There are two ways to explain something: say what "brought it about", or describe it at a more "fundamental" level. For example, a cat displayed on a computer screen can be explained, more "fundamentally", as there being certain voltages in bits of metal in my screen, which in turn can be explained, more "fundamentally", as that there are certain subatomic particles moving in a certain way. If we keep explaining the world in this way and reach a point at which no more "deeper" explanations can be given, then we would have found some facts which are brute or inexplicable, in the sense that we cannot give them an ontological explanation. As it might be put, there may exists some things that just are. The same thing can be done with causal explanations. If nothing made the big bang expand at the velocity it did, then this is a brute fact in the sense that it lacks a causal explanation.