Ni/Se: this is how quality x manifests, and so can we determine the extent to which any person/thing possesses said quality, if at all.
-purely inductive and holistic; qualities are discrete and internally anchored, like a tape reel, or one of those comic books where flipping through the pages conveys the story.
Si/Ne: this is how we've seen quality x manifest, and these are the different circumstances within which it will manifest, to greater or lesser degrees.
--purely deductive and interpolative; qualities are seen as reflections of more basic recursions that are equalized by the subject through the environment.
Ni/Se is seeking a singular context within which to describe things. I remember telling gilly once, that based on the manner in which this person manifested a certain quality, I could know with certainty that his friends could very well be my friends. Ne would've speculated on how that quality manifests in others, to find various 'proofs' of its internal correlates. Ni seeks to seal the boundaries within the environment so that subjective impressions can be seamlessly streamed, ideas given form and substance.
Si/Ne is more about encompassing various experiential contexts; there is no 'right' answer here, or definitive manifestation of a given quality/behavior. when I was in the swiss antique store, the objects took me where they did internally, based on the feel and immediate impact they created; to Ne/Si, the journey is through the impressions and intuitions about the historical context within which they existed, there is no distinct feel, but a variegated sense of how different people could have enjoyed them, and how their present condition bears on the usage of items with similar internal qualities.