Most languages use Latin alphabet, and the English language is the only one that does not include diacritical marks.
Vietnamese is a tonal language. Accents are used to denote six distinctive tones: “level” (ngang), “acute-angry” (sắc), “grave-lowering” (huyền), “smooth-rising” hỏi, “chesty-raised” (ngã), and “chesty-heavy” (nặng). In writing, one tone is represented as unmarked (a), four are indicated with diacritics marked on a vowel (á, à, ả, and ã), and one is marked with a dot under a vowel (ạ). Let’s break down these individual tone marks.
An unmarked tone (ngang) has no accent. Its pitch ranges from mid to high-mid.
An acute (dấu sắc) is a forward-slash accent placed on vowels: á, é, í, ó, ú, and ý. An acute, which starts from a narrow bottom and ends with a wide top, denotes a high rising pitch. It should rise slightly toward the right of the base character (á) without falling off. When combined, it must be positioned clearly from another mark (ắ, ấ, ế, ố, ớ, or ứ).
A grave (dấu huyền) is a backward-slash accent placed on vowels: à, è, ì, ò, ù, and ỳ. A grave, which starts from a wide top and ends with a narrow bottom, denotes a low pitch. It should rise slightly toward the left of the base character (à) without falling off. When combined, it must be positioned clearly from another mark (ằ, ầ, ề, ồ, ờ, or ừ).
A hook above (dấu hỏi) is a tone mark that resembles a dotless question mark placed on vowels: ả, ẻ, ỉ, ỏ, ủ, and ỷ. It denotes a mid-low dropping pitch. When combined, it must be positioned clearly from another mark (ẳ, ẩ, ể, ổ, ở, or ử).
A tilde (dấu ngã) is an accent placed on vowels: ã, ẽ, ĩ, õ, ũ, or ỹ. It denotes a high rising pitch. When combined, it must be positioned clearly from another mark (ẵ, ẫ, ễ, ỗ, ỡ, or ữ).
An underdot (dấu nặng) is a dot placed under vowels: ạ, ẹ, ị, ọ, ụ, and ỵ. It denotes a low dropping pitch and must be positioned clearly below the baseline.