Diacritical marks may appear above or below a letter, or in some other position such as within the letter or between two letters.
The main use of diacritical marks in the Latin script is to change the sound-values of the letters to which they are added.
This varies from language to language, and may vary from case to case within a language.
Examples are the diaereses in the borrowed French words naïve and Noël, which show that the vowel with the diaeresis mark is pronounced separately from the preceding vowel; the acute and grave accents, which can indicate that a final vowel is to be pronounced, as in saké and poetic breathèd; and the cedilla under the "c" in the borrowed French word façade, which shows it is pronounced .
In Gaelic type, a dot over a consonant indicates lenition of the consonant in question.
The tittle (dot) on the letter i of the Latin alphabet originated as a diacritic to clearly distinguish i from the minims (downstrokes) of adjacent letters.
It first appeared in the 11th century in the sequence ii (as in ingeníí), then spread to i adjacent to m, n, u, and finally to all lowercase i's.
In other alphabetic systems, diacritical marks may perform other functions.
Vowel pointing systems, namely the Arabic harakat ( ), which, respectively, mark abbreviations or acronyms, and Greek diacritical marks, which showed that letters of the alphabet were being used as numerals.French treats letters with diacritical marks the same as the underlying letter for purposes of ordering and dictionaries.The Scandinavian languages, by contrast, treat the characters with diacritics ä, ö and å as new and separate letters of the alphabet, and sort them after z.Because of vowel harmony, all vowels in a word are affected, so the scope of the diacritic is the entire word.In abugida scripts, like those used to write Hindi and Thai, diacritics indicate vowels, and may occur above, below, before, after, or around the consonant letter they modify.In some cases, letters are used as "in-line diacritics", with the same function as ancillary glyphs, in that they modify the sound of the letter preceding them, as in the case of the "h" in the English pronunciation of "sh" and "th".