front unrounded vs ü front rounded and ı back unrounded vs u back rounded). The close-mid vowels ö, o are not involved in vowel harmony processes. Front/back harmony Turkish has two classes of vowelsfront and back. Vowel harmony states that words may not contain both front and back vowels. Therefore, most grammatical suffixes come in front and back forms, e.g. Türkiye'de "in Turkey" but Almanya'da "in Germany". Rounding harmony In addition, there is a secondary rule that i and ı in suffixes tend to become ü and u respectively after rounded vowels, so certain suffixes have additional forms. This gives constructions such as Türkiye'dir "it is Turkey", kapıdır "it is the door", but gündür "it is the day", karpuzdur "it is the watermelon". Exceptions Not all suffixes obey vowel harmony perfectly. In the suffix -(i)yor, the o is invariant, while the i changes according to the preceding vowel; for example sönüyor – "he/she/it fades". Likewise, in the suffix -(y)ken, the e is invariant: Roma'dayken – "When in Rome"; and so is the i in the suffix -(y)ebil: inanılabilir – "credible". The suffix -ki exhibits partial harmony, never taking a back vowel but allowing only the front-voweled variant -kü: dünkü – "belonging to yesterday"; yarınki – "belonging to tomorrow". Most Turkish words do not only have vowel harmony for suffixes, but also internally. However, there are many exceptions. Compound words are considered separate words with respect to vowel harmony: vowels do not have to harmonize between members of the compound (thus forms like |gün "this|day" = "today" are permissible). Vowel harmony does not apply for loanwords, as in otobüs – from French "autobus". There are also a few native modern Turkish words that do not follow the rule (such as anne "mother" or kardeş "sibling" which used to obey vowel harmony in their older forms, ana and karındaş, respectively). However, in such words, suffixes nevertheless harmonize with the final vowel; thus annesi – "his/her mother", and voleybolcu – "volleyballer". In some loanwords the final vowel is an a, o or u and thus looks like a back vowel, but is phonetically actually a front vowel, and governs vowel harmony accordingly. An example is the word saat, meaning "hour" or "clock", a loanword from Arabic. Its plural is saatler. This is not truly an exception to vowel harmony itself; rather, it is an exception to the rule that a denotes a front