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Diacritics

In the polytonic orthography traditionally used for ancient Greek and katharevousa, the stressed vowel of each word carries one of three accent marks: either the acute accent (ά), the grave accent (ὰ), or the circumflex accent (α̃ or α̑). These signs were originally designed to mark different forms of the phonological pitch accent in Ancient Greek. By the time their use became conventional and obligatory in Greek writing, in late antiquity, pitch accent was evolving into a single stress accent, and thus the three signs have not corresponded to a phonological distinction in actual speech ever since. In addition to the accent marks, every word-initial vowel must carry either of two so-called "breathing marks": the rough breathing (ἁ), marking an /h/ sound at the beginning of a word, or the smooth breathing (ἀ), marking its absence. The letter rho (ρ), although not a vowel, also carries rough breathing in a word-initial position. If a rho was geminated within a word, the first ρ always had the smooth breathing and the second the rough breathing (ῤῥ) leading to the transliteration rrh.

The vowel letters ⟨ α, η, ω ⟩ carry an additional diacritic in certain words, the so-called iota subscript, which has the shape of a small vertical stroke or a miniature ⟨ ι ⟩ below the letter. This iota represents the former offglide of what were originally long diphthongs, ⟨ ᾱι, ηι, ωι ⟩ (i.e. /aːi, ɛːi, ɔːi/), which became monophthongized during antiquity.

Another diacritic used in Greek is the diaeresis (¨), indicating a hiatus.

This system of diacritics was first developed by the scholar Aristophanes of Byzantium (c. 257 – c. 185/180 BC), who worked at the Musaeum in Alexandria during the third century BC. Aristophanes of Byzantium also was the first to divide poems into lines, rather than writing them like prose, and also introduced a series of signs for textual criticism. In 1982, a new, simplified orthography, known as "monotonic", was adopted for official use in Modern Greek by the Greek state. It uses only a single accent mark, the acute (also known in this context as tonos, i.e. simply "accent"), marking the stressed syllable of polysyllabic words, and occasionally the diaeresis to distinguish diphthongal from digraph readings in pairs of vowel letters, making this monotonic system very similar to the accent mark system used in Spanish. The polytonic system is still conventionally used for writing Ancient Greek, while in some book printing and generally in the usage of conservative writers it can still also be found in use for Modern Greek.

Although it is not a diacritic, the comma has a similar function as a silent letter in a handful of Greek words, principally distinguishing ό,τι (ó,ti, "whatever") from ότι (óti, "that").