The expression 'unwritten doctrines' (in Greek, ἄγραφα δόγματα, ágrapha dógmata) refers to doctrines of Plato taught inside his school and was first used by his student Aristotle.
The Tübingen School is sometimes called the Tübingen School of Plato studies to distinguish it from an earlier 'Tübingen School' of theologians based at the same university.