Why did the Eccie metaphysician stop in the middle of intercourse with Emmy?
Because he realized that while they had successfully established the substance, they were still deeply conflicted about the accidents—and they couldn't proceed until they determined if the "union" was a real relation or just a mental construct.
Of course the Eccie metaphysician’s reviews all started with “This is just a dream…” And ends with “…then I woke up.”