[Grammar] John is writing Mary a letter. = John is writing a letter to/for Mary.

[sitifan]

1. John is writing Mary a letter.
2. John is writing a letter to Mary.
3. John is writing a letter for Mary.

#1 and #2 have basically the same meaning. Can #1 sometimes have the same meaning as #3?

 

[Rover_KE]

#3 is more likely to mean that John is writing a letter on Mary's behalf because she is unable or unwilling to write it herself.