What is the name of this grammatical phenomenon?

Question

I have observed that many native English speakers (esp. American English, in my experience) tend, within the same sentence, to start a new clause whose subject is an element of the previous clause. Here is an example: > That is what fascinated me about programming—is that it changes the way you think about the world. In this sentence, "what fascinated me about programming" is used as an object in the first clause, but then gets reused as the subject of the second clause. Other examples: - > This is something we talk about a lot—is the size of the community is substantially smaller than the React community [...] ([source](https://www.youtube.com/watch?v=LCNs92YQjhw#t=3m05s)) - > This is what I think went wrong is what Trump did very effectively is tap the angst and the anger and the hurt and the pain that millions of working-class people are feeling. ([source](https://www.youtube.com/watch?v=zlmuKtyhDKg&t=59s)) I have only noticed this phenomenon in spoken English, as opposed to written English. What are its name and origins? Note: I'm aware of the *double copula* (a.k.a. "double is"); this is related, but different.

Answer 1

The oral and written way people speak is often not interchangeable. Many people will write much better than they speak because they see writing as a more formalized way of communication that will be more heavily critiqued. At the same time spoken language is much more lax and people often use improper grammar when speaking because it sounds more fluid and is sometimes easier to say.

Answer 2

This phenomenon is called psuedocleft, but the phrase usually begins with something like what, where, why or who and is meant to emphasize the 2nd half of the sentence, for example: What she is eating for lunch, is a hamburger. If the sentence starts with It, then the phenomenon is called a cleft.

Although I am sure you have heard them, I find the examples you have given to be grammatically incorrect or very awkward at best! The point of the double copula is also to emphasize the second half of the sentence, but it is wholly unnecessary! In my opinion, starting the sentence with a clause already gives the second half emphasis.

Here is how I would change your examples:

1. That is what fascinated me about programming; it changes the way you think about the world. Or if you must make one a dependent clause of the other ... What fascinated me about programming, is that it changes the way you think about the world. [pseudocleft]
2. Something we talk about a lot is the size of the community, which is substantially smaller than the React community Or It is the size of the community that is what we talk a lot about, which is substantially smaller than the React community. [cleft]

You can find more interesting terms and definitions here: https://ygdp.yale.edu/glossary