Calling a fact brute is a curious mix of the obvious and utterly obscure. In the philosophical discussions of the last few years, it means just “an inexplicable fact”, and so it does no more than negate the possibility of an explanation, or at least to negate any explanation by extrinsic causes (like agent causes). The word “brute” even frequently becomes the focus of attention, and so there are actually articles that parse degrees of brutishness or describe facts as relatively brute. But why focus on such a seemingly arbitrary word when “inexplicable” would do just as well?
Brute seems more like an idol or a totem. The brute is what is irrational and overpowering – the bête noire that lurks in the background. Brute is meant to give a fundamental character to things as just there but not as manifest or self evident. The mind sees nothing but is simply bound or overcome by a force that makes no sense and is incapable of doing so.
Brute facts thus seem more like a mythology, or at least a total view of explanation. The idea is that explanation itself at some point breaks down, becomes ridiculous, or no longer functions while at the same time there is some given that must be held to. There is, however, another crucial element – for the failure of explanation cannot be a mystery, that is, a sublime or superintelligible reality. “Bruteness” indicates a harshness or violence against the intellect, a frustration in the reaching for a goal while the solemn and lofty character of mystery is a direct negation of this sort of frustration.
And so we hang onto brute because it alone conveys the dark mythology of fundamental frustration.