I am not a pure linguist but rather at the intersection of computational linguistics, NLP and computer science. Thus please be cautious with me and my ignorance. I am looking for definitions of sentence complexity - possibly with respect to information / entropy. For example, a matrix sentence like
The washing machine which is on top of the shelf is running is clearly more complex than
The washing machine is running. So one naive way of defining one sentence is more complex than another would be counting how many sentences are recursively incorporated. Another way would be counting the length of the sentence. My question would be, is there any formal work on defining this more thoroughly? I would very much appreciate any hints!
I found these things so far, writing this to make sure references don't repeat and for own documentation purpose:
Lexical Density (Chapt. 5 and 6)
Measuring syntactic complexity (here, curiousdannii suggests to look at morphology. I haven't seen anything on it. I wonder if morphology is relevant considering I am only looking at English.)