Answer:
- We use the pronoun 'he' to replace a name in a particular sentence.
For instance, instead of saying "John has a dog", we could say "He has a dog"
- We use 'him' when we replace a name in a sentence which is used as an object.
We could either say "The dog belongs to John", or "The dog belongs to him". (Note that in this case, the dog is the subject, and John (he) is the object)
- It is now easy to understand the difference between 'who' and 'whom': the difference between these two pronouns is the same as the difference between 'he' and 'him'. 'Who' replaces a subject - a person that performs the action, while 'whom' replaces an object.
For instance, we could ask: "Who has a dog?", but we would say "I am not sure whom this dog belongs to."