[821 verses](article sg masc nom)  "The" is the Greek definite article, hos, ("the").   It usually precedes a noun or changes the word it precedes (adjective, infinitive, participle, etc.) to act like a noun. When not preceding a a word that can become a noun, takes the meaning of "the one" or, in the plural, "the ones." Proper nouns do normally not take articles but they are needed when the noun ending cannot be changed to show the noun's role in the sentence as an object, indirect object, or genitive (possessive) form. However, the Greek article is very close to "this" so the purpose of an article like this can also be demonstrative.There is no vocative definite article, (despite being shown in Perseus). When the vocative is meant, no article is used or they used ω or ε.  See this article.  -- The word translated as "the" is the Greek definite article, "the," which usually precedes a noun or changes the word it precedes (adjective, infinitive, participle, etc.) to act like a noun. The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those") than the English "the." See this article for more.