Early Dialogues:
Apology, Charmides, Crito, Euthyphro, Alcibiades, Hippias Major, Hippias Minor, Ion, Laches, Lysis
Middle Dialogues:
Cratylus, Euthydemus, Gorgias, Menexenus, Meno, Phaedo, Protagoras, Symposium,
Middle or Late Dialogues:
Republic, Phaedrus, Parmenides, Theaetetus
Late Dialogues:
Clitophon, Timaeus, Critias, Sophist, Statesman, Philebus, Laws
This is slowly falling out of favor, and I think this is a good thing. We know from Aristotle that the Laws was definitely written after the Republic. Internal evidence makes it highly probable that Parmenides, Phaedrus, the Republic, and Theaetetus were written in the same phase and that Critias, Timaeus, the Laws, Philebus, the Sophist, and the Statesman are all from the same phase of writing, because these two groups have very close links even on minor points of style. And that's getting about to the limit of what we can actually be said to know about whether the dialogues are really 'early' or 'late'. No Plato scholar I've ever met takes this ordering very seriously as even a roughly chronological ordering, although many seem to have their own pet scheme that they play around with. The major reason that I think this way of ordering the dialogues has survived, and probably will for quite some time, is that it makes a sort of sense even independently of any chronological questions. All the 'early' dialogues are very, very Socrates-oriented. All the 'late' dialogues are much more independent of Socrates. The 'middle' dialogues are appropriately in-between. Thus it made a sort of tempting sense as a progression from Plato mostly defending Socrates (early) to Plato doing his own thing (late). But outside the two groupings noted above, that's more of an attractive imaginative picture than anything else.
The traditional scheme for the dialogues is rather different, and goes back to Thrasyllus of Mendes, the first collector of the collected works of Plato. We know of Thrasyllus's scheme from Diogenes of Laertius. It was common for Greek dramatic works to come in tetralogies -- for instance, three tragedies and a satyr play. So Thrasyllus ordered the dialogues in tetralogical sets:
First Tetralogy
Euthyphro, Apology, Crito, Phaedo
Second Tetralogy
Cratylus, Theaetetus, Sophist, Statesman
Third Tetralogy
Parmenides, Philebus, Symposium, Phaedrus
Fourth Tetralogy
Alcibiades, Second Alcibiades, Hipparchus, Rival Lovers
Fifth Tetralogy
Theages, Charmides, Laches, Lysis
Sixth Tetralogy
Euthydemus, Protagoras, Gorgias, Meno
Seventh Tetralogy
Hippias Major, Hippias Minor, Ion, Menexenus
Eighth Tetralogy
Clitophon, Republic, Timaeus, Critias
Ninth Tetralogy
Minos, Laws, Epinomis, Epistles
There are a number of nice features about these groupings, although there seems to be no general principle governing them. The First Tetralogy constitute a sort of Last Days of Socrates: in Euthyphro, Socrates is heading to his trial, in Apology he is at his trial, in Crito he is awaiting his death, and in Phaedo he is on the verge of it. A number of other links are noticeable, but a number of possible links don't show up. The Theatetus has very little obviously to do with the First Tetralogy, for instance, but the dialogue is clear enough that, in internal chronology at least, the Euthyphro occurs only a little later than the Theatetus, and it is made so clear that Plato seems to have thought it important somehow. We get no sense from the way these are grouped of how Gorgias serves as a near-perfect thematic bridge between the death dialogues of the First Tetralogy and the Republic (one of many, many reasons why I think Gorgias is the single most essential Platonic dialogue to have read).
The classical Neoplatonists developed their own canons of Plato. One, usually attributed to Iamblichus, selected out twelve dialogues of special importance. Like practically everything in Neoplatonism, it was structured as an ascent. We start with Alcibiades, on the subject of knowing oneself, and sort of expand from there into the entire cosmic order:
Alcibiades
Gorgias
Phaedo
Cratylus
Theaetetus
Sophist
Statesman
Phaedrus
Symposium
Philebus
Timaeus
Parmenides
There are other possible ways to group the dialogues. One interesting one that I've seen is that of Bernard Suzanne, a Plato enthusiast:
Overview of tetralogies | a i t i a (cause) | epithumiai (desires) phusis (nature) | thumos (will) krisis (judgment) èthos (behavior) | logos (reason) kosmos (order) | ||
| Tetralogy 1 : The start of the quest what is man ? | ALCIBIADES man | LYSIS friendship (philo-) | LACHES manhood (andreia) | CHARMIDES wisdom (-sophos) | ||
| Tetralogy 2 : The sophists eikasia (conjecture) | PROTAGORAS relativism | HIPPIAS Major illusion of beauty | HIPPIAS Minor illusion of the "hero" | GORGIAS illusion of logos | ||
| Tetralogy 3 : Socrates' trial pistis (true belief) | MENO pragmatism | EUTHYPHRO letter of the law | THE APOLOGY OF SOCRATES law in action | CRITO spirit of the law | ||
| Tetralogy 4 : The soul psuchè | THE SYMPOSIUM the driving force : eros | PHÆDRUS nature of the soul : erôs<=>logos | THE REPUBLIC behaviour of the soul : justice | PHÆDO destiny of the soul : being | ||
| Tetralogy 5 : Speech (logos) dianoia (knowledge) | CRATYLUS the words of speech | ION logos of the poet | EUTHYDEMUS logos of the sophist | MENEXENUS logos of the politician | ||
| Tetralogy 6 : Dialectic epistèmè (science) | PARMENIDES the traps of reason | THEÆTETUS the limits of reason | THE SOPHIST the laws of reason | THE STATESMAN the goals of reason | ||
| Tetralogy 7 : Man in the world kosmos (order) | PHILEBUS the good of man | TIMÆUS contemplating (theôria) | CRITIAS deciding (krisis) | THE LAWS acting (erga) |
This is a very nonstandard organization, but this kind of Neo-Neoplatonist approach to reading the dialogues (that is, in the sense of seeing them as a unified philosophical curriculum) has much to recommend it; as Suzanne argues, taking the dialogues in this way lets one see them all together as forming a sort of super-dialogue on the subject of what it is to live a philosophical life.
In my reading of the dialogues I won't be able, for scheduling reasons, to follow any rigorous order. But I like the idea, found in the Neoplatonists and Suzanne, of starting with Alcibiades. Currently my thought is that I might get some of the obvious spurious dialogues out of the way in the next week or so, and then come June start with Alcibiades, the Rival Lovers, and Charmides. (Charmides' authenticity is undisputed; Alcibiades is usually regarded as authentic, although after Schleiermacher argued that it was spurious in the nineteenth century it went through a disputed period, and its authenticity is still occasionally disputed; Rival Lovers is usually regarded as spurious, although Julia Annas has argued that the case against it is very weak.) But that might change a bit.
