original_query: What is the difference between the diaeresis and the umlaut diacritical marks?
query: What is the difference between the diaeresis and the umlaut diacritical marks?
answer: The diaeresis indicates that two adjacent vowels should be pronounced as separate syllables, while the umlaut indicates a sound shift, typically where a back vowel becomes a front vowel.  Although they look identical in modern usage, they represent different phonological phenomena.