the vowel alternates (sometimes with an added suffix) indicating a different tense-aspect. Navajo vowel ablaut, depending on the verb, may be a change in vowel, vowel length, nasality, and/or tone. For example, the verb stem 'to handle an open container' has a total of 16 combinations of the 5 modes and 4 aspects, resulting in 7 different verb stem forms (i.e. , , , , , , ). Another verb stem | 'to cut' has a different set of alternations and mode-aspect combinations, resulting in 3 different forms (i.e. , , ): Prosodic apophony Various prosodic elements, such as tone, syllable length, and stress, may be found in alternations. For example, Vietnamese has the following tone alternations which are used derivationally: Albanian uses different vowel lengths to indicate number and grammatical gender on nouns: English has alternating stress patterns that indicate whether related words are nouns (first syllable stressed) or verbs (second syllable stressed). This tends to be the case with words in English that came from Latin: Prosodic alternations are sometimes analyzed as not as a type of apophony but rather as prosodic affixes, which are known, variously, as suprafixes, superfixes, or simulfixes. Consonant apophony Consonant alternation is commonly known as consonant mutation or consonant gradation. Bemba indicates causative verbs through alternation of the stem-final consonant. Here the alternation involves spirantization and palatalization: Celtic languages are well known for their initial consonant mutations. Indo-European linguistics Indo-European ablaut In Indo-European linguistics, ablaut is the vowel alternation that produces such related words as sing, sang, sung, and song. The difference in the vowels results from the alternation (in the Proto-Indo-European language) of the vowel e with the vowel o or with no vowel. To cite a few other examples of Indo-European ablaut, English has a certain class of verbs, called strong verbs, in which the vowel changes to indicate a different grammatical tense-aspect. As the examples above show, a change in the vowel of the verb stem creates a different verb form. Some of the verbs also have a suffix in the past participle form. Umlaut In Indo-European linguistics, umlaut is the vowel fronting that produces such related words as foot > feet or strong > strength. The difference in the vowels results from the influence of an , or (which in most cases has since been lost) at the end of the word causing the stem vowel to be pulled