How is Bulgarian related to Macedonian, Serbo-Croatian, and Slovene?

Bulgarian is a South Slavic language that shares a common heritage with Macedonian, Serbo-Croatian, and Slovene, all of which evolved from the same linguistic roots.123

Relationship to Macedonian

Bulgarian and Macedonian are most closely related to each other. Both languages contrast with other Slavic languages by having lost noun case declension and by placing the definite article after the noun or adjective. While they share significant linguistic features, their modern standard forms diverged in the 20th century; eastern Macedonian dialects gradually transition into Bulgarian, whereas western Macedonian dialects are more distinct.241

Relationship to Serbo-Croatian and Slovene

These languages belong to the South Slavic subgroup but are categorized differently from the Bulgarian-Macedonian group.15
* Serbo-Croatian: While distinct, some Serbian dialects (specifically the Prizren-Timok group) share features with certain North Macedonian and West Bulgarian dialects. Historically, all these languages were influenced by local variants of Old Church Slavonic.53
* Slovene: Slovene shares some commonalities with the Kajkavian dialects of Croatia and exhibits traces of historical links to West Slavic languages like Czech and Slovak.5