Gravity is a fact (or maybe a set of facts) which can be observed and measured. But why it operates as it does, and even in some respects what it does in some situations are beyond the objective knowledge from observation. Newton's classical laws as related to gravity are useful in most real world situations even today, but when we get into far-out physics his description seems to break down, or at least not cover. And the "why" I suppose will be forever a mystery.

Dave Oesterreich