What we might call the logical iron triangle of revelation, involving Tradition, Scriptures, and Magisterium, uses theological reasoning guided by the Holy Spirit to safeguard the purity of the deposit of faith. Vatican II’s Dei Verbum helps us distinguish between the requirements of Catholic doctrinal accuracy (including those of the ordinary Magisterium) and the usefulness of theological speculation. Doctrines—requiring Catholic assent—have theological roots that extend from the Magisterium through Tradition to Sacred Scripture.