Creating Morphology: the Case

This is a big one. Case may not be uncommon, but people can struggle coming to grips with it. The grammatical case of a noun shows us what role that word has in the sentence. English has only a few instances of this, limited to the use of personal pronouns. Look at the following English sentence:

He hugs him

In this sentence we know that somebody (he) hugs someone else (him), so if we substitute 'he' with Tom and 'him' with John, we will have

Tom hugs John

So we know that Tom is the subject of the sentence and John is the object. That is to say, it's Tom doing the hugging, not John. John is in fact receiving it. So if we go back to he and him, we know that 'he' is doing the hugging and 'him' is receiving the hugging. 'He' is the subject of the sentence and 'him' is the object.