The Copula Cycle

In languages that do this, you can get funny sent things like I, he the doctor means I am the doctor. As a verb moves from its sort of original meaning into a copula sense, it may retain traces of its original sense. Another source of copulas are demonstratives and third person pronouns. And then over time what will happen is, or can happen is the pronoun or demonstrative will be invented to take up the slack.