"Mirroring the
special composition question is the Simple Question.
[1] It asks what the jointly necessary and sufficient conditions are for
x to be a mereological simple. In the literature this question explicitly concerns what it is for a material object to lack proper parts, although there is no reason why similar questions cannot be asked of things from other
ontological categories.
There have been many suggested answers to the Simple Question. Answers include that
x is a simple if and only it is a point-sized object; that
x is a simple if and only if it is indivisible; or that
x is a simple if and only if it is maximally continuous. Kris McDaniel has argued that what it is for an object to be a simple is a matter of brute fact, and that there is no non-trivial answer to the Simple Question (2007b)."
Notice that even the contemplation of "simple philosophical question" is not simple. It's an entire philosophical school of thought.
So...not simple.