NC starts out with 4 pages of quite general considerations about recursive functions and grammars, but then he becomes a more specific and defines his 4 classes of grammars that today could be called general [type 0], context sensitive [type 1], context free [type 2] and regular [type 3]. The last three are defined in terms of restrictions on the grammatical rules they use which implies diminishing power of how large a language they can generate.
About 2 pages are used to find languages that is in one type but not in the next so it is a proper inclusion.

There is very little proper linguistics – max 1 page in total. NC seems to conclude that real languages are between type 1 and 2 but NC to say there is no natural restriction on the allowed grammatical rules that will define them. If I had more time I should like to read more on this.

NC uses the term Markov Finite State Machines, but there is no probability in his definition.