One is a straight factual (empirical) question. Who killed JFK? That can be answered, exactly and certainly, from observation and evidence (conspiracy theories notwithstanding).
Two: Why did Oswald kill JFK? Also a factual question, it cannot be answered with similar exactitude and certitude, requiring interpretation of evidence. That’s qualitatively different.
I’m of the former view. An isosceles triangle doesn’t exist in nature. The idea of it is a human construct. Yet one embodying the way existence works. That statement is not a matter of observation but, rather, of deducing how existence must work. A universe where that’s not so is inconceivable. Not just by limited human minds, but inconceivable in principle.* Thus our discoveries of mathematical truths are discoveries about the fabric of reality.
So the foregoing question types all concern reality. But “reality” itself can be a slippery concept. Berlin discusses the philosophy of Bishop Berkeley (pronounced Barkley, 1685-1753).
Did he really? What he actually said is hard to untangle. Berlin tries, calling Berkeley the ultimate empiricist, holding that what we get from our senses is all there is. If we can’t see it, touch it, smell it, etc., it isn’t there. Yet Berkeley believed in the spiritual (God and all that). How could this be reconciled? He posited (in Berlin’s words) “eternal souls or spirits . . . whose existence does not depend . . . on being sensed, or being otherwise the content of someone’s experience.” In other words, nothing exists outside sensory perception — except when it does. That’s how religion scrambles the brain.
Some modern voices still tell us nothing exists outside our brains — which don’t really exist either. I’ve deconstructed such nonsense here: https://rationaloptimist.wordpress.com/2016/12/10/is-reality-real/
It’s true that the reality we perceive is, to a great extent, constructed within our minds. A simple example: a rose is not actually “red.” At the level of its molecules, atoms, and quarks, you will find no redness.
Our senses do have limitations in perceiving reality. Even science has a tough time modeling it. A bowling ball seems a solid object, but again at the subatomic level there’s nothing solid. Yet if you drop it on your foot, it sure behaves as solid.
Thus there is a lot of reality in our perception of bowling balls and other objects. Otherwise our lives would be impossible. The fact that our senses do guide us pretty successfully through the world’s reality proves both that that reality is real and that our senses are pretty good at registering it.
With that settled (;-)) we can finally move on to the fourth kind of question. While the others do raise philosophical issues (as discussed), the fourth kind are entirely philosophical. Which, Berlin wrote, “cannot be answered by either observation or calculation, by either inductive methods or deductive; and . . . those who ask them . . . do not know where to look for the answers.” Berlin calls the first three types “factual” (or empirical) and the fourth “formal.”
Yet “what is time?” actually has a certain empiricalness. It’s not unanswerable in principle. We actually have a common sense understanding, and physicists have teased out nuances beyond that. Time is an element of the reality of existence.
So I would call all the foregoing descriptive questions, as distinguished from prescriptive questions. The latter to include ones like how we should live, how we relate to others, how we find meaning in life, etc. The methods for seeking answers are very different than with descriptive questions. There is something about existence that would describe how time works, even if we don’t have the words or concepts to embody it. But there’s no such something that could resolve prescriptive puzzles.
The Enlightenment was an intellectual revolution starting around three centuries ago. Its core was rationalism — believing in use of reason to understand existence and enabling us to improve it. And this did coincide with great leaps in human understanding, through science, through mathematics and logic, and rationalist philosophy. In Berlin’s telling, the Enlightenment’s enthusiasts envisioned that continued progress along such lines would ultimately answer all questions, including the fourth kind. This he called an “heroic attempt to make philosophy a natural science.”
But Berlin is not denigrating Enlightenment thinkers. “A very great deal of good was done,” he says, “suffering mitigated, injustices avoided or prevented, ignorance exposed, by the conscientious attempt to apply scientific methods to the regulation of human affairs.” Their “intellectual power, honesty, lucidity, courage and disinterested love of the truth . . . remain to this day without parallel.” And if their greatest goal proved “delusive,” Berlin thinks far worse of the nineteenth century reaction, with “implications that were, both intellectually and politically, more sinister and oppressive.” He’s referring to the romanticism that sacralized the “nation” and “state” as some supreme force trumping the Enlightenment’s morality premised on the individual. That romanticist movement was the wellspring of all the millennial and utopian “isms” that would wrack the twentieth century.
* One can construct non-Euclidean geometries, internally logical. I cannot say whether a non-Euclidean universe could actually work. But if so, that would not contradict what I’ve written. We’d still have a cosmos wherein certain mathematical laws — whatever they may be — are baked in. A cosmos with no such laws baked in would be an impossible chaos.