Based on a large group of features, the Macedonian dialects can be divided into Eastern and Western groups (the boundary runs approximately from Skopje and Skopska Crna Gora along the rivers Vardar and Crna). In addition, a more detailed classification can be based on the modern reflexes of the Proto-Slavonic reduced vowels ("yers"), vocalic sonorants and the back nasal (o). That classification distinguishes between the following 5 groups :
- Ohrid - Prespa Group consisting of the Lower Prespa region, Ohrid, Struga, Radožda and Vevčani.
- Debar Group consisting of the Drimkol - Golobrdo region, Debar, Mala Reka, Reka, Gora, and Skopska Crna Gora.
- Polog Group consisting of Gostivar (Upper Polog), and Tetovo (Lower Polog), as well as the entire West Central region (Prilep, Kičevo, Bitola, Kruševo, Florina/Lerin)
- Kostur - Korča Group consisting of KorçNestorioë (Korča), Kastoria (Kostur), and Nestorio (Nestram).
- Eastern Group consisting of the entire eastern part of the Macedonian region including the w:Kumanovo - w:Kriva Palanka, w:Štip - w:Strumica, w:Tikveš - w:Mariovo, Maleševo - Pirin, Lower Vardar (Kilkis/Kukuš, Edessa/Voden-Pella/Postol, Thessaloniki/Solun), and the Serres/Ser - Gotse Delchev/Nevrokop subregions.
It must be noted that the Ser-Nevrokop group is in fact located mostly outside of the Republic of Macedonia (in Greece and Bulgaria, respectively) and hence its identification as a group of "Macedonian" dialects is an especially controversial issue. Bulgarian linguists regard both as East Bulgarian dialects, more specifically as part of a Rupski dialect group that stretches through Southern w:Thrace up to the w:Black Sea . In Greece, all Slavic varieties spoken in the northern part are referred to simply as slavic, except the local Macedonian population does call their local language "Makedonski"
Variation in vowels
The vocalic inventories of the West Central dialects consist of five vowels, /i, ɛ, a, ɔ, u/. Most of the remaining dialects also have phonemic /ə/. In addition, phonemic /ɑ/, /æ/, and /y/ and vocalic /l/ and /r/ occur in various dialects.
Most dialects have /ɛ/ from original ě (w:yat), but the Eastern region is characterised by the development of ě to /a/ after /c/: Eastern cal, Western cel (whole). Besides that, in easternmost Aegean Macedonia and the w:Blagoevgrad Province of w:Bulgaria ě gives /a/ or /æ/ under stress. In the dialects of Aegean Macedonia, this happens regardless of the environment, whereas the dialects of the Blagoevgrad province have (just like standard Bulgarian and its eastern dialects) /a/ if there is a back vowel in the following syllable, and /ɛ/ if there is a front vowel. For example, 'white' (sing. - plur.) sounds in the following way in these dialects: Serres-Drama: /bala/ - /bali/, Suho and Visoka: /bæla/ - /bæli/, Nevrokop: /bala/ - /bɛli/. In Korca, ě becomes /iæ/ under stress.
Variation in consonants
As far as consonantal features are concerned, the entire Western region is distinguished from the East by loss of /x/ (except Tetovo, Gora and Korča) and the loss of /v/ in the intervocalic position (except Mala Reka and parts of Kostur-Korča): /glava/ (head) = /gla/, /glavi/ (heads) = /glaj/. The Eastern region preserves /x/ (except Tikveš-Mariovo and Kumanovo-Kriva Palanka) and intervocalic /v/. The East is also characterised by the development of epenthetic /v/ before original /o/ where the West has epenthetic /j/: Eastern /vaglɛn/ (coal) but Western /jaglɛn/. The diphonemic reflexes are most characteristic of the dialects of Aegean Macedonia and Blagoevgrad province, Kostur-Korča and Ohrid-Prespa. The Serres-Nevrokop dialects have a series of phonemically palatalised consonants.
Variation in word stress and its effects on vowels
The Western dialects generally have fixed stress, antepenultimate in the Republic of Macedonia, and penultimate in Greece and Albania. The Eastern region, along with the neighbouring Bulgarian dialects, has various non-fixed stress systems. In Lower Vardar and Serres-Nevrokop unstressed /a, ɛ, ɔ/ are reduced (raised) to [ə, i, u]. The reduction of unstressed vowels (as well as the aforementioned allophonic palatalisation of consonants) is characteristic of East Bulgarian as opposed to West Bulgarian dialects, so these dialects are regarded by Bulgarian linguists as transitional between East and West Bulgarian ..