A locus (plural loci) is a "place" or topic — one of the standing headings under which theology has traditionally been organised. Melanchthon's Loci Communes (1521) fixed the term for Protestant use, but the divisions are much older. A rough, conventional list:
- Prolegomena — what theology is, and how it is known (revelation, Scripture, reason).
- Theology proper — the doctrine of God: existence, attributes, Trinity.
- Anthropology — humanity as created, fallen, and bound; sin and the image of God.
- Christology — the person and natures of Christ.
- Soteriology — the work of Christ and the application of salvation: grace, faith, justification, sanctification.
- Pneumatology — the person and work of the Holy Spirit.
- Ecclesiology — the Church, ministry, and sacraments.
- Eschatology — the last things: death, resurrection, judgment, the age to come.
The order is not accidental — each locus tends to assume the ones before it. How you answer under anthropology (how bound is the fallen will?) quietly settles a great deal under soteriology (how does grace reach it?).
That dependency is exactly what the Disputed Questions try to make visible.