In general, irregular forms of German verbs exist to make for easier and clearer pronunciation, with a vowel sound in the centre of the word the only part of the word that changes in an unexpected way (though endings may also be slightly different). This modification is often a moving of the vowel sound to one pronounced further forward in the mouth. This process is called the Germanic umlaut. However, a number of verbs including "sein" (to be) are fully irregular, as in English "I am" and "I was" sound completely different.