used to show that the second vowel in a makes a distinct sound and is therefore not a diphthong.
when is an Apostrphe used?
when a preposition ends with a vowel and the next word begins with a vowel, the final vowel of the first word drops out. This is called "elision". it is marked by and apostrophe. Similar to an english contraction.
what is an elision?
when a prepostion ends with a vowel and the next word begins with a vowel.
When are Accents used?
in almost every Greek word. it is placed over a vowel and shows which syllable receives the accent.