+0
Sir,

Is the verb "let" is modal verb?

1. Let him go to play.
2. Let him play.

Which one is correct?

Thanks.
+0
No, not a modal. It is a 'coercive' verb (I just learned)-- what I would have called a polite command.

Both of your sentences are correct, or, many would say 'let him go play'.
Comments  
Site Hint: Check out our list of pronunciation videos.
Sir,
Let's go to see a movie.
Let's go see a movie.

Whic one is correct?
Thanks.
The first is more formally acceptable, but the second is also widely used, especially in the US. For more discussion, please Go talk.