I recently read a passage from Kenneth R. Westphal's Realism, Science, and Pragmatism that read:
Or imagine, following Stout (1938-39), someone in a room which is supported by foundations which no one perceives. What the person perceives--i.e. the room--is actual, but the foundations either do not exist (idealism), or are at best mere unfulfilled possibilities (phenomenalism). But how could something actual be supported by unfulfilled possibilities (or even something non-existent)? It seems that this would lead us to reject many of our ordinary casual and other explanations.
What I don't quite understand is why the idealist/phenomenalist cannot logically infer that since the room he is in is not collapsing, there must be supports underneath the flooring. My question is this: cannot an idealist/phenomenalist have knowledge of unobserved entities through logical inference from his experiences?