Is a Topic a Normal Part of a Sentence?

In languages that are topic prominent is a sentence ungrammatical if it doesn't have a topic in it or is it just very ambiguous or vague? That depends 100% on context. In some ways, a topic is not a normal part of your sentence. It's a linguistic event that limits the applicability of the statement you're about to make. So either there's already an existing discourse topic floating around. Or you're introducing something new. We had one interesting conlang that we looked at a month or two ago that would look to me like switch topic but I've never seen a natural language that has something like that.