There are many kinds of Modals, and very many more important Transformations to be learned.
Modals express other notions too. For example:
- I may go (permissibility)
- I might go (possibility)
- I should go (responsibility)
- I could go (opportunity)
- I would go (opportunity)
- I can go (capability)
It's no wonder that English as a second language is very illusive and frustrating, but as a first, for children, it seems simple and natural.
The list of transformations to be learned are very long.
When sentences are conjoined ("I went to the store and bought a cookie"); or embedded ("I, jumping headlong into my car, rushed off the store.") or turned into relative clauses ("I, who just bought my car, drove recklessly to the store.") they are instances of transformations.
Another important one is the Passive Transformation. For example, "I paid the clerk." is transformed into "The clerk was paid by me."