Unlike neighbouring Slavic languages, Slovak retained only six out of seven Proto-Slavic grammatical cases. The vocative merged with the nominative, but it has been preserved in archaic forms of some words related to family, e.g. "otec" → "otče", "syn" → "synu", "kmotor" → "kmotre" (O father/son/godfather) and to address God: "Boh" → "Bože", "Ježiš" → "Ježišu", "Kristus" → "Kriste" (O God/Jesus/Christ). Slovak retained basic principles of declension, but the evolution of declension paradigms had been strongly affected by the principle of analogy: less frequent declension suffixes were replaced by more frequent suffixes from other cases and paradigms. The outcome of this process was simplification and higher uniformity of declension patterns. This process was more intense compared to Czech. The independent development of Slovak naturally resulted in unique declension patterns.