Philosophy is the branch of human knowledge that deals with boundaries through definition. A good philosophical debate is one that is had with basic questions of being and just paradigms. What version of the universe sounds correct essentially.
Basic questions in philosophy include questions about the cosmic paradigm about what is fair and just. This is where religion and atheism clash the most.
A just question would be such as this: is reincarnation just and fair? So then a debate would be had about this idea.
I'm going to list a few more fundamental questions, but keep in mind all of these questions have an ultimate answer that is right. That is the quest of the philosopher, to find the answer for everyone and to present it to them. Proof is in the argument, because some things don't require evidence to be proven, only a perfect argument.
Is the afterlife real?
Do we come from somewhere before we are born?
Do we reincarnate, and if so, where?
What is the nature of the afterlife and why should we care?
Are there divine beings in higher dimensions?
Are there any higher dimensions?
Should anyone even ask any of these questions openly?
Is it safe to be philosophical?
Should we have open inquiry or closed inquiry?
Should anyone be allowed to be philosophical?
Is philosophy dangerous to a sound mind and able disposition?
When should someone be allowed to study philosophy?
Who should make the decision (any decision really)?
As you can see philosophy can lead you to some pretty dangerous places. These are just a few of the thousands if not millions of questions that make up the bulk of what we call philosophical reasoning. Every one of these questions has an answer that requires no pre-conception to know (that's when you are born knowing the answers). You can reason your way through anything really. But we must always be aware that philosophy has it's time and it's place and again I generally feel no one under 50 should get terribly philosophical much less metaphysical. This world takes precedent over whimsical musings even if they happen to be right on.