The Sanskrit and Latin did not develop any article at all, and the Greek never developed the indefinite usage to any extent. Moreover, the Greek was slow in creating the definite article, though in Homer we do have the beginning of the article. The forms ο, η, το are occasionally used in Homer with the force of “the,” chiefly with adjectives, proper names, or for contrast. It is just in Homer that we see the evolution of the article, for this same form ο, η, το is very common here as a demonstrative and appears also as a relative. Hence ο is originally a demonstrative that was gradually weakened to the article or heightened to the relative. This threefold usage of one form is seen in Ionic, for Herodotus uses the τ form as demonstative and relative as well as for the article. And even in Attic ο is preserved occasionally as demonstrative. So in the poets and Plato the demonstrative ο appears before relative pronouns (cf. Justin Martyr).
The modern Greek often has ο οπιος as the relative like old English “the which.” In the poetical quotation in Acts 17:28 του γαρ και γενος εσμεν we have the demonstrative του.
εν αυτω γαρ ζωμεν και κινουμεθα και εσμεν ως και τινες των καθ υμας ποιητων ειρηκασιν του γαρ και γενος εσμεν
for in Him we live, and move, and are; as also certain of your poets have said: For of Him also we are offspring.
Such uses of ο δε are common, when the demonstrative is in contrast with a noun usually in an oblique case. So ο δε ειπεν (Mat 14:18)
ο δε ειπεν φερετε μοι αυτους ωδε
And he said, `Bring you them to me here.’
So also in the contrast expressions οι μεν, οι δε (Acts 14:4)
εσχισθη δε το πληθος της πολεως και οι μεν ησαν συν τοις ιουδαιοις οι δε συν τοις αποστολοις
And the multitude of the city was divided, and some were with the Jews, and some with the apostles,
In Act 5:41, οι μεν is used absolutely.
οι μεν ουν επορευοντο χαιροντες απο προσωπου του συνεδριου οτι υπερ του ονοματος αυτου κατηξιωθησαν ατιμασθηναι
they, indeed, then, departed from the presence of the sanhedrim, rejoicing that for his name they were counted worthy to suffer dishonour,
We even have ο as a relative in the expression ο ην (Rev 1:4) in harmony with Homeric usage.
ιωαννης ταις επτα εκκλησιαις ταις εν τη ασια χαρις υμιν και ειρηνη απο του ο ων και ο ην και ο ερχομενος και απο των επτα πνευματων α εστιν ενωπιον του θρονου αυτου
John to the seven assemblies that are in Asia: Grace to you, and peace, from Him who is, and who was, and who is coming, and from the Seven Spirits that are before His throne,
The Greek relative ος, η, ο which is common in Homer and in the later Greek is demonstrative in origin also. So in John 5:11 we read ο δε απεκριθη, and in Rom 14:2 ος μεν πιστευει.
ο δε απεκριθη αυτοις ο ποιησας με υγιη εκεινος μοι ειπεν αρον τον κραββατον σου και περιπατει
And he answered them, `He who made me whole that one said to me, Take up your couch, and be walking;’
ος μεν πιστευει φαγειν παντα ο δε ασθενων λαχανα εσθιει
one does believe that he may eat all things–and he who is weak doth eat herbs;
Compare ος μεν, ος δε in Rom 4:5
ος μεν κρινει ημεραν παρ ημεραν ος δε κρινει πασαν ημεραν εκαστος εν τω ιδιω νοι πληροφορεισθω
One judges one day above another day, and another judges every day alike ; let each in his own mind be fully assured.
The contrasted expressions are found in oblique cases as ον μεν, ον δε (Luke 23:33).
και οτε απηλθον επι τον τοπον τον καλουμενον κρανιον εκει εσταυρωσαν αυτον και τους κακουργους ον μεν εκ δεξιων ον δε εξ αριστερων
and when they came to the place that is called Skull, there they crucified him and the evil-doers, one on the right hand and one on the left.
This demonstrative in both forms is the same word as the Sanksrit demonstrative sa, sa, tad, where in the masculine and feminine nominative singular the t has been softened to s. So in Greek, this s becomes often a rough breathing, (τ)ο, (τ)η, το, and this form then loses the accent. We see it in the Latin is-te, is-ta, is-tud, the Gothic sa, so, thata, German der, die, das, the Anglo-Saxon se, seo, thaet, and modern English this, that. In the German and the English we have also the threefold use of the same form as demonstrative, article, relative. English “the” is a weakened form of “this.” But in the New Testament as in the earlier Attic ο, η, το is usally the article and the demonstrative and relative ideas are generally expressed by other words. But the demonstrative use of ο continues in the modern Greek as το και το, this and that. The modern Romance languages obtained their articles from the Latin demonstratives ille, iste.