Who does what: the idea of case πτώσεις

In English, word order tells you who does what: the father loves the son is not the son loves the father. Greek works differently. The ending of a noun shows its job in the sentence, so the words can come in almost any order.

English still has a trace of this: he sees him, she sees her. The form changes with the job. Greek does this with every noun, adjective and article. These different forms are called cases.

The two cases to meet first: the nominative is the subject (who does it), and the accusative is the direct object (who or what it is done to). The little word for "the" changes too: ὁ is nominative, τόν accusative.