"Protagoras" is often considered one of the last of the "early dialogues". Three dialogues are often considered "transitional" or "pre-middle": "Euthydemus", "Gorgias", and "Meno". Proponents of dividing the dialogues into periods often consider the "Parmenides" and "Theaetetus" to come late in the middle period and be transitional to the next, as they seem to treat the theory of Forms critically ("Parmenides") or only indirectly ("Theaetetus"). Ritter's stylometric analysis places "Phaedrus" as probably after "Theaetetus" and "Parmenides", although it does not relate to the theory of Forms in the same way. The first book of the "Republic" is often thought to have been written significantly earlier than the rest of the work, although possibly having undergone revisions when the later books were attached to it.