[NB. This post is rated PG ("Pedagogical Guidance") for indictments of the infallible authority of reference works and for scandalizing references to literary critical theory. It is probably best not to read this if you are in Latin 101. If you are in Latin 201, please use discretion.]
Part the Second, in which our heroine discovers the shocking origins of "syllabus" and rekindles her hermeneutic of fiery suspicion towards lexica.
Now, like most people, I don't like being wrong. But I'm willing to be wrong if that's a stop on the way to discovering the truth -- even about something as seemingly petty as the proper declension of the word "syllabus". Mostly, I was embarassed to admit that I'd never looked the thing up before. So I got out my chunky lexica and went to work, beginning with the reference my advisor had sent.
Here is what L&S (Lewis & Short) say (s.v. "syllabus"):
syllabus, -i, m., = σύλλαβος, a list, register, syllabus, Aug. Conf. 13, 15.
From this, the word seems to be a Greek loaner, clearly 2nd declension. Augustine uses it. And thus the plural is indubitably "syllabi".
The only problem with this is that L&S is wrong.
I know this seems a rather arrogant assessment. The very fact that I continued to search betrays a deep lack of wanting to eat crow. But, in my defense, I trusted the scholars who told me the word was 4th declension and I was wondering where they got this idea.
So I looked up this Greek word σύλλαβος in my LSJ (Liddel, Scott, Jones -- it's the big one, the "Great Scott"). It's not there because the Greek word does not exist. A quick search on the TLG confirmed this. Greek authors through the Byzantine period aren't using this phantom word σύλλαβος (all the hits for σύλλαβοι, σύλλαβοις, etc. are verbal forms of συλλαμβάνω (roughly, "gather"). There is a Greek noun συλλαβή; it's feminine and means (roughly) "syllable".
But there was still this Augustine citation. So I looked it up (basically to check whether it was in a form that might betray its being 2nd as opposed to 4th declension). The form in the Confessions is "syllabis", which actually leaves open the question of whether it's 1st or 2nd declension. It's more likely to be 1st, in my opinion -- from the 1st declension Latin borrowing from Greek συλλαβή (Latin form is the expected "syllaba"). And this particularly because it's meaning is most probably "syllable". Augustine is talking about the angels in heaven and writes "ibi legunt sine syllabis temporum". Considering that ancient reading is often aloud, that makes rather a nice point -- the angels read without temporal syllables, syllables which sound within space-time. [Amusingly, one could posit that the angels are doing everlasting reading courses: they read without the syllabi/syllabuses/syllabūs of time!]
Curiouser and curiouser... I checked the OLD (Oxford Latin Dictionary) for "syllabus"; no entry there. I was now beginning to wonder where the word itself came from, let alone its plural! So I looked at the OED (Oxford English Dictionary) entry for the English word "syllabus".
Here's a summary of what it says: The existence of the word "syllabus" appears to be founded on a suspect reading in Cicero's Epistle ad Atticum IV. iv, where the reading Latin is sillybous (Gk. σιλλύβους). And some editors still print this (like Purser, whose text is on Perseus and the editor of the Loeb vol., Winstedt). However, the word appears in the mss. at ad. Att. 4.5 and 4.8 as "sittybis" (NB. Purser and Winstedt, inter alios, print these again as "sillybis"). Cicero is clearly using the words to mean something like "title slips" -- bits of parchment with tables of contents or titles to be glued on to scrolls or scroll cases to identify the contents of the volume. Cicero petitions Atticus to send him some slaves to work as gluers and to find him some nice parchment suitable for use as "title slips".
So, I then did some TLG searches. The Greek σίλλυβον seems to refer to a thorny or "fringy" type of flower. And σίττυβα can be either some sort of dish or a small leather thing (perhaps a chamois? or a shrug?). Clearly the latter, as associated with animal skins, is much more likely to be a word used for "title slip". Note, also, that this latter Greek word is feminine and first declension!
So here is my reconstruction of the history of "syllabus":
1) Around 68 B.C., Cicero borrows the Greek word σίττυβα and transliterates it as sittyba; he uses the inflected forms sittybis (dat/abl. pl.) and sittybas (acc. pl.)
2) At some point in the manuscript tradition, between 68 B.C. and 1389 (when the Codex Mediceus was copied) the first of these (at least) is corrupted to sillybos, with a change both of gender and of the t's to l's. It is possible that the corruption was first to sillybas and then a further change was made to the gender of sillybas when a copyist compared Greek forms of σίλλυβον (a neuter noun) and mistook it for masculine; hence the masculine acc. pl. in Latin as sillybos.
3) In 1389, the copyist of the Codex Mediceus 49,18 writes "sillabos", continuing the errors of gender and of double-L for double-T, but introducing the further change of -a- for -y-. This may have been an attempt at correction, although there is no Greek word beginning σίλλαβ- (according to what's extant and in the TLG database).
4) After 1389, a further change occured for one of two reasons: 1) the fact that the Greek meaning of σίλλυβον is so dissimilar from that of the intended σίττυβα prompted a reconsideration of the Latin "sillybus" OR 2) the error of the Codex Mediceus reading "sillabos" prompted the "correction" also of the first vowel to make it seem like a transliteration of a real Greek word (since no Greek word in σίλλαβ- was known). Therefore, in an effort to correct a corrupt reading, philologists decided it was not meant to represent the Greek σίλλυβον, but rather, that the error had been a phonetic transposition and that "sillybos" should read "syllabos" -- as a transliteration of the (non-existent) Greek word σύλλαβος, derived from συλλαμβάνω.
5) In the late 15th and early 16th centuries, printed editions of Cicero's letters adopted the reading "syllabos" (e.g. Cratander, Jenson, and the Roman ed. of 1470). This word "syllabus" was then, in fact, adopted as a 2nd declension masculine noun in Neo-Latin and its meaning extended to the needs of Latin-speaking academics (who no longer used scrolls requiring "title slips"). On the logic of a derivation from συλλαμβάνω, the word "syllabus" came to mean something like "list" (i.e. something gathered and collated). This isn't too far off from the original meaning of "title slip" -- although the original term used by Cicero refers to the material of the title slip (leather, skin) and not to the function of the title slip (a list of collected titles). On this basis, therefore, the proper plural of "syllabus" would seem to be "syllabi".
6) In recent years, before I was taught such things in the 1990's, another stage of philological hyper-correction observes that if the word has been derived as a nomen actionis from the Greek συλλαμβάνω, it should logically follow the rules for such verbals. They generally take the -u- marker (often as -tus or -sus, but Greek loan-words frequently come in without the dental). Therefore, the word, IF it were derived from συλλαμβάνω, should be 4th declension with plural syllabūs.
1) The plural of "syllabus" is most correctly "syllabi".
2) Never just believe what teachers tell you. And don't always believe lexica either; they're composed by other human beings just like you and me. And often those other human beings had less resources available to them because they were living back before the Internet when dinosaurs roamed the earth and all research was done with notecards, fountain pens, train rides and letters of introduction by more senior scholars. They had lots of more important things to do than to make sure they got a totally correct definition for really rare words -- they had to worry about Lewis Carroll taking nude photos of their kids in verdant settings and other serious things like that.
3) If you want to join the syllabūs camp, you're certainly welcome to. But you should realize that since "syllabus" isn't an "organic" Latin word in the first place, you won't be proving much of anything about your intelligence. Rather, by taking the silly thing seriously, you will merely be complicit in the tyranny of l'écriture. Because let's face it: this whole etymological history and the very existence of the word "syllabus" is the sort of thing which serves as intellectual pornography for deconstructionists.