In contemporary philosophy, a brute fact is something that cannot be explained. 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, the fact that there's a cat on my computer screen can be explained, more "fundamentally", as the fact that there are certain voltages in bits of metal in my screen, which in turn can be explained, more "fundamentally", as the fact 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 have found some facts which are brute or inexplicable, in the sense that we cannot give them an ontological explanation. As we might put it, we have some things that just are. We can do the same thing with causal explanations. If nothing made the big bang explode at the velocity it did, then this is a brute fact, in the sense that it lacks a causal explanation.