- The cat sat on the mat.
- She hit him.
These are direct objects. The following are indirect objects:
- The dog brought Jane his lead.
- I sent my son a letter.
The structure of these sentences is (S/V/O/O) where S = subject, V = verb and O = object. The first object is an indirect object, the second is a direct object. Notice that, in the last example, you sent a letter, not your son. The sentence makes perfect sense without the indirect object.
An equivalent sentence to the last example is:
- I sent a letter to my son.
Here some grammarians also see son as the indirect object (letter is the term which cannot be left out).p720
- McArthur, Tom (ed) 1992. The Oxford companion to the English language. Oxford University Press.