
Karl H. answered 03/18/19
I'm a young, energetic, and professional teacher and writer.
Hi Jenni,
These words are indeed different, and are not to be used interchangeably. However, the meanings are closely related. I'll try to explain.
"Ding" and the plural form "Dinge" are the terms with the broadest meaning. A "Ding" is a "thing." Just as in English, we can call almost anything a "thing", so too in German. But obviously, calling something a "thing" doesn't say that much about it."Gegenstand" and "Sache" are both "things" of a particular sort.
A "Gegenstand" is an object. As we would say in English: "X is the object of desire" or "the object of perception." We could say, perhaps, that a "Gegenstand" is a thing that stands in relation to something else: as an object of desire stands in relation to someone who desires it. Additionally, "Gegenstand" is a definite thing. A room can be filled with "Gegenstände", and this means that the room is filled with discrete, definite things, like sofas, chairs, tables, lamps.
"Sache" has a more slippery meaning. A "Sache" can be like a "subject-matter" or an "issue." "Die Sache selbst" is a German phrase meaning "the matter at hand." But a "Sache" can also be a personal belonging, or an item in one's possession. I wouldn't say "Meine Dinge" or "Meine Gegenstände" to refer to my possessions. I would say "Meine Sachen." Additionally, "meine Sache" in the singular can refer to one's personal cause or life-project, as would say in English that someone has committed herself to the cause of women's rights.
I hope this answer helps!