{ 1 } - a necessary truth.
{ 2 } - a contingent truth.
{ 3 } - an illusion.

While the world surely exists, it might not have existed. We could imagine there not having been any world at all. Just as each particular being in the world exists contingently, so too the existence of the world seems to be a contingent matter.

Also, the world is composed of temporal and destructible beings. If everything in the world were destroyed, then the world would cease to be. Thus the world can't be a necessary being. So the world is contingent.

So, by the principle of sufficient reason, we can ask "Why is there a world at all?" -- and expect that there is some sort of answer.