Dr. Kreeft's point, building off of C.S. Lewis' work on the character and weaknesses of modernism as well as his own work, is that there are really only three possible relationships between an individuals epistemology (the study of what is know and how it can be know) and ontology (the study of being or of what is). Either there are more things in heaven and earth (in reality) than are dreamt of in their philosophy (their epistemology), there are the same number of things in heaven and earth than are dreamt of in their philosophy, or there are fewer things in heaven and earth than are dreamt of in their philosophy. Crudely speaking - and I am already anticipating a few grumpy notes from post-modernists out there- the post-modernist holds that there are fewer things; the modernist, that there are the same number of things; and the pre-modernist, that there are more things in heaven and earth.
For the post-modern, reality is a really tricky concept (and possibly an entirely meaningless word) to begin with. The post-modern approach tends to downplay reality as unknowable and therefore unreal. For many, many reasons, they have abandoned anything like a correspondence theory of truth (truth is when a proposition corresponds to reality) and then operate out of a desire to establish ones own "working" reality which they seem to simultaneously think must also be a fundamental illusion. However it plays out it will work out to a belief that reality, to the extent that it is a meaningful word, is smaller than the conceptions of each individual.
The modernist holds on to that initially exciting yet ultimately deadening idea that human achievement will one day be able to explain absolutely every aspect of reality and offer something like a scientific proof to verify those explanations. You hear lines like "if science can't prove it then it doesn't exist" from them. Here in America we have a very common religious form of this modernism which claims instead "if the Bible doesn't prove or affirm it then it isn't real". Both are modernist by this model. The claim boils down to the belief that human reason is capable of explaining or describing every aspect of being; that there are exactly as many things in heaven and earth as are dreamed of in philosophy. Thus prior to meeting the ghost, Horatio is a sort of proto-modernist.
But the pre-modern believes that there are more things in Heaven and Earth than are dreamt of in his philosophy; that reason works but isn't comprehensive. The pre-modern believes there is more to the world than what we can figure our. This does not mean (as I find many athiest apologists have construed it) that the pre-modernist gives up on trying to understand or that they believe that reality can't be known. "It is the glory of God to conceal a thing; but the honour of kings is to search out a matter." (KJV) Instead, the pre-modernist believes that there is always going to be more to know, that reality is fuller, more complex, more meaningful, more beautiful than we can comprehend - there will always be more to discover.
That is why I named the blog "More things in Heaven and on Earth". By now you must know that I am, or at least am trying to become, a pre-modern. Thus the title reflects my belief in infinite depth and breadth of the universe, of reality, of the cosmos, of the question and of the answers. There is bottomless joy in the search for truth because the truth is always being found and will never be exhausted.