The period from 387 to 361 BC The major difference between these texts and his earlier works is that he tends toward grander metaphysical themes and begins to establish his own voice in philosophy. Socrates still has a presence, however, sometimes as a fictional character. In the Meno for example Plato writes of the Socratic idea that no one knowingly does wrong, and adds the new doctrine of recollection questioning whether virtue can be taught. In the Phaedo we are introduced to the Platonic doctrine of the Forms, in which Plato makes claims as to the immortality of the human soul. The middle dialogues also reveal Plato's method of hypothesis.