The main use of diacritical marks in the Latin script is to change the sound-values of the letters to which they are added. 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 /s/ rather than /k/. In other Latin-script alphabets, they may distinguish between homonyms, such as the French là ("there") versus la ("the") that are both pronounced /la/. In Gaelic type, a dot over a consonant indicates lenition of the consonant in question.
In other alphabetic systems, diacritical marks may perform other functions. Vowel pointing systems, namely the Arabic harakat ( ـِ ,ـُ ,ـَ, etc.) and the Hebrew niqqud ( ַ◌, ֶ◌, ִ◌, ֹ◌, ֻ◌, etc.) systems, indicate vowels that are not conveyed by the basic alphabet. The Indic virama ( ् etc.) and the Arabic sukūn ( ـْـ ) mark the absence of vowel. Cantillation marks indicate prosody. Other uses include the Early Cyrillic titlo stroke ( ◌҃ ) and the Hebrew gershayim ( ״ ), which, respectively, mark abbreviations or acronyms, and Greek diacritical marks, which showed that letters of the alphabet were being used as numerals. In the Hanyu Pinyin official romanization system for Chinese, diacritics are used to mark the tones of the syllables in which the marked vowels occur.
In orthography and collation, a letter modified by a diacritic may be treated either as a new, distinct letter or as a letter–diacritic combination. This varies from language to language, and may vary from case to case within a language. English is the only major modern European language requiring no diacritics for native words (although a diaeresis may be used in words such as "coöperation").
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".
Among the types of diacritic used in alphabets based on the Latin script are:
The tilde, dot, comma, titlo, apostrophe, bar, and colon are sometimes diacritical marks, but also have other uses.
Not all diacritics occur adjacent to the letter they modify. In the Wali language of Ghana, for example, an apostrophe indicates a change of vowel quality, but occurs at the beginning of the word, as in the dialects ’Bulengee and ’Dolimi. 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.