Students of Modern Greek meet forms like στον, στου, στις, στα, etc., very soon as they improve studying Greek, and ponder on two things: 1. What is the meaning of these forms? and 2. Why are they so ordinary?

1. What is the meaning of these forms?

The meaning of these small words is understood efficiently if we respond to the following question: why do they all begin with a sigma? The explanation is, that they are all a union of a preposition + some type of the definite article, in any incident apart from the nominative. Take for example, στον: the preposition part is the original σ-, and the article is -τον (accusative, masculine, singular, in harmony to the above table). The complete type of the preposition was εις in the not-so-distant past, and it meant “in”. (Up till the late 1970’s, Greek publications were until now using εις.) So the complete type used to be “εις τον”. But the εις got decreased to a single σ out of erosion, because of its informal usage, and was united with the article ensuing it into one unit. Thus, εις + τον > ’ς + τον > στον. Precisely the same occurred to all the other types of the definite article, but not in the nominative case. (So, even though the nominative of the masculine is ο, there is not anything like σο.) It’s undemanding to comprehend why this worked only in the other cases apart from the nominative: for the reason that the ancient/obsolete preposition εις was anticipating either genitive or accusative case to succeed it (or even the now-terminated dative), but not ever nominative. But why? Once again, it’s simple to see that, too: what is the sense of εις τον? In English, we would translate it as “in the”, right? Well, if we had a case method for articles in English, you would see that the “the” would be represent in the accusative case — it’s solely rational to do so. Certainly, think about that in the only condition where cases still endure in English, i.e., in pronouns, we state “in her”, which is accusative/dative (“There’s somewhat in her that produces her…”), not *“in she”, which could be the nominative case. So, “in” is not followed by nominative, even in English. Ditto in Greek, apart from that the Greek case method is living, and transparent. 

2. Why these words are so ordinary?

There is a reason for that, too, and it is as follows. English uses many prepositions to distinguish in what way a noun is connected to one more noun. For example, we say: “the book is on the table”, “the fork is in the drawer”, “the child is at household”, “dad moves to the church”. In difference, Greek fits into the “Spanish school” in how it sees the connections among nouns: it sees them in a easy way (easier than English). So, just like the Spanish talkers use only “en” in their language (meaning “in”, and for that purpose they usually use erroneously “in” when they communicate in English in all kinds of cases where they could practice “on”, “at”, or “to”), ditto with Greek, which used to use only εις (“in”) in the former, and so following εις turned into obsolete, the language was left with the different forms of στ-.