The man spoke too fast to be understood.

[sitifan]

1. The man spoke too fast to be understood. (quoted from a textbook)
2. The man spoke too fast to understand him.
3. The man spoke too fast to understand.
4. The man spoke too fast for me to understand him.
5. The man spoke too fast for me to understand.
Are #2, #3, #4 and #5 grammatically correct?

 

[tedmc]

1 and 4 are correct.

 

[jutfrank]

The problem with 2 and 3 is not really the grammar but that they don't make sense. 4 and 5 are both okay.

 

[sitifan]

6. The tea is too hot to drink it.
7. The tea is too hot to drink.
Are #6 and #7 both okay?

 

[5jj]

Only #7 works.