Introduction To Christianity - pg. 109

The question to which everything finally leads could be
formulated like this: In all the variety of individual things
what is, so to speak, the common stuff of being - what the
one being behind the many "things", which nevertheless
all "exist"? The many answers produced by history can finally be
reduced to two basic possibilities. The first and most obvious
would run something like this: Everything we encounter is
in the last analysis stuff, matter; this is the only thing
that always remains as demonstrable reality and consequently
represents the real being of all that exists - the materialistic solution.
The other possibility points in the opposite direction. It says:
Whoever looks thoroughly at matter will discover that it is
being-thought, objectivized thought. So it cannot be the ultimate.
On the contrary, before it comes thinking, the idea; all
being is in the last resort being-thought and can be traced back
to mind as original reality; this is the "idealistic" solution.