the perfective verb being created out of the imperfective by adding a prefix or making a stem change. The imperfective aspect typically indicates that the action is unfinished, in progress, or repetitive; while the perfective aspect typically denotes that the action was completed, instantaneous, or of limited duration. Some Štokavian tenses (namely, aorist and imperfect) favor a particular aspect (but they are rarer or absent in Čakavian and Kajkavian). Actually, aspects "compensate" for the relative lack of tenses, because aspect of the verb determines whether the act is completed or in progress in the referred time. Phonology Vowels The Serbo-Croatian vowel system is simple, with only five vowels in Shtokavian. All vowels are monophthongs. The oral vowels are as follows: The vowels can be short or long, but the phonetic quality does not change depending on the length. In a word, vowels can be long in the stressed syllable and the syllables following it, never in the ones preceding it. Consonants The consonant system is more complicated, and its characteristic features are series of affricate and palatal consonants. As in English, voice is phonemic, but aspiration is not. {| class="wikitable" |- ! Latin script ! Cyrillic script ! IPA ! Description ! English approximation |- ! colspan="6" | trill |- | style="text-align:center;"| r | style="text-align:center;"| р | style="text-align:center;"| | alveolar trill | rolled (vibrating) r as in carramba |- ! colspan="6" | approximants |- | style="text-align:center;"| v | style="text-align:center;"| в | style="text-align:center;"| | labiodental approximant | roughly between vortex and war |- | style="text-align:center;"| j | style="text-align:center;"| ј | style="text-align:center;"| | palatal approximant | year |- ! colspan="6" | laterals |- | style="text-align:center;"| l | style="text-align:center;"| л | style="text-align:center;"| | alveolar lateral approximant | light |- | style="text-align:center;"| lj | style="text-align:center;"| љ | style="text-align:center;"| | palatal lateral approximant | roughly battalion |- ! colspan="6" | nasals |- | style="text-align:center;"| m | style="text-align:center;"| м | style="text-align:center;"| | bilabial nasal | man |- | style="text-align:center;"| n | style="text-align:center;"| н | style="text-align:center;"| | alveolar nasal | not |- | style="text-align:center;"| nj | style="text-align:center;"| њ | style="text-align:center;"| | palatal nasal | British news or American canyon |- ! colspan="6" | fricatives |- | style="text-align:center;"| f | style="text-align:center;"| ф | style="text-align:center;"| | voiceless labiodental fricative | five |- | style="text-align:center;" | z | style="text-align:center;" | з | style="text-align:center;" | | voiced dental sibilant | zero |- | style="text-align:center;"| s | style="text-align:center;"| с | style="text-align:center;"| |