Traditionally the usage of the particle ὦ followed by the vocative phrase is described in context of the texts as follows :
In Attic ὦ is regularly added to the vocative phrase of direct address.
By the omission of ὦ the vocative phrase may express hostility, wrath, grief, contempt, etc.
In this paper, however, I research the usage of ὦ in Sophocles syntactically in order to describe what function ὦ may have.
ὦ tends to be used with the vocative phrase ;
(1) when an address term (i.e. the vocative) is an adjective and a participle without a substantive.
(2) when a vocative phrase has more than two constituents.
(3) when an address term in a vocative phrase has more than two attrbutives.
(4) when a vocative phrase stands between the first metron and the third metron in a line, especially when a monosyllabled-address term appears on the arsis of the third metron.
Therefore it is considered that ὦ is not a mere particle or interjection to the vocative, but ὦ may also have the syntactic function to distinguish the vocative phrase from a complete sentence.