Good question, as many people are still confused when it comes to English Grammar Rules. ‘Who’ and ‘Whom’ are two of the words that they have a tough time with. The word ‘whom’ is the cause of the problem. So much so that some teachers and English scholars do not even use the word. Here goes, The word ‘who is always the subject of the sentence, while ‘whom’ is the object. Example, ‘Who is there’? Versus ‘Whom did you see there’? In the first sentence ‘who’ is the subject. And in the second sentence ‘you’ is the subject and ‘whom’ is the direct object of the subject.