To express a location or a direction in modern Greek, you have to use the preposition "σε" (= "in" or "to", depending on the context).
After this preposition, the word that follows has to be in accusative case.
Here's how the definite articles change in accusative:
- ο -> το(ν) (sing. masc.)
- η -> τη(ν) (sing. fem.)
το -> το (sing. n.)
οι -> τους (pl. masc.)
- οι -> τις (pl. fem.)
- τα -> τα (pl. n.)
To say "in the'' or "to the" in Greek, you have to combine the preposition "σε" and the definite article of your choice in accusative:
- το(ν) -> στο(ν)
- τη(ν) -> στη(ν)
το -> στο
τους -> στους
- τις -> στις
- τα -> στα
I hope that this helps. :-)
Well, there is an actual rule for that.
When the articles/pronouns are followed by a vowel or κ, π, τ, μπ, ντ, γκ, ξ, and ψ, the -ν is used.
When the articles/pronouns are followed by β, δ, γ, φ, θ, χ, μ, ν, λ, ρ, σ, or ζ, the -v is omitted.
This rule is now for feminine articles/pronouns only.
Reading many posts I realized that native English speakers have problems with these kinds of prepositions. I am not a Greek speaker, but as a native Spanish speaker I want to say something that might help.
The word μέσα is an adverb (and not a preposition). As such, it can be used to modify verbs:
Εγώ είμαι μέσα (I am inside)
If you want to give more information you have to use the correct preposition according to the type of additional information:
Εγώ είμαι μέσα στο σπίτι (I am inside * the house)
The thing is that in English the word "inside" is an adverb, a preposition and also a noun. In the first example, the word "inside" works like an adverb. In the second one it works like a preposition. English doesn't need an "extra" preposition in order to introduce the complement "the house" because "inside" is the preposition. Other languages, like Spanish, require "extra" preposition because the word "dentro (inside)" is an adverb. In fact a typical mistake we make when we are learning English is say: "I am inside to/of the house" As far as I know the same thing happen in Greek. In all examples where people keep asking about the "σε" it seems the confusion arises from the fact that they think the word before "σε" is the preposition, but usually is an adverb. Almost all the greek words in the "tips" section are adverbs.
I think you can say the same thing (in context) in Greek without using the adverb "inside" if you use the correct preposition (in this case "σε"):
Εγώ είμαι στο σπίτι. (I am in the house)
In this case, there is no doubt about the "σε". Σε is more important that μέσα because σε is the preposition.