Four Core Vocative Patterns

Al-Munādā: Vocative Types and Rules

Proper name / intended indefinite: “yā Zaydu / yā rajulu” — built, accusative position.
Construct: “yā ʿAbda llāhi” — accusative.
Quasi-construct: “yā ṭāliʿan jabalan” — accusative.
Unspecified indefinite: “yā rajulan” — accusative.

These are the four central patterns; special forms follow.