The octopus is an animal which has served the BBC well as a topic for news reports, the main ingredient of exotic recipes, and as a worthy subject for usage advice:

Besides showing that the BBC at times seems to give self-contradictory advice, the quotations suggest that the word octopus has three possible plurals in English: octopuses, octopi, and octopodes. To descriptivists, using any of the three forms is equally correct – to prescriptivists, at least some of the plurals are better than others.

According to the HUGE Database of Usage Guides and Usage Problems that Robin Straaijer and I are working on in the context of the Bridging the Unbridgeable project, the first to give guidance on the usage of octopus is Henry Watson Fowler. Fowler, in his Dictionary of Modern English Usage (Oxford, Clarendon Press 1926), advises the reader to use octopuses. Indeed, of the twelve usage guides in the database that include recommendations on the plural of octopus, all but one are of the same opinion: octopuses. Both octopi and octopodes are usually proscribed, the latter because even though it is ‘good Greek’, it sounds ‘pedantic’.

Some usage guides give advice in the form of a little rhyme, such as Patricia O'Conner in Woe is I (1996):

Rhymes on usage like this – O'Conner's book contains several others – aim to offer the reader a handy memory aid. The question that arises, of course, is whether such an aid, or any usage advice at all, really has an effect on people's daily use of English.

To see how large the gap between language advice and actual usage is, I consulted three corpora: the British National Corpus, the Corpus of Historical American English, and the Corpus of Contemporary American English.Footnote ² In all three, the plural octopuses proved most popular, with octopi as its runner-up. Octopodes hardly occurs at all, so actual usage more or less matches the advice given by most usage guide authors.

If we turn to two major English dictionaries, the Oxford English Dictionary (OED) and the Merriam Webster Dictionary (MER),Footnote ³ we see that they provide a different, seemingly more descriptive, view on the topic than most usage guides do. The OED gives both -i and -uses as unmarked plural inflections, while it marks octopodes as ‘rare’:

In its interactive online entry, MER also gives octopuses and octopi as plurals. It is tempting to think that the advice from these dictionaries is closer to actual usage and therefore better than that given in the usage guides, for the former acknowledge that both octopi and octopuses are in use – as indeed my corpus search confirmed. However, at the point of writing this article, there were as many as 44 comments to the MER entry, which illustrates that people are still on the look-out for the single, most acceptable form:

Interestingly, the most recent comment (number 44) – “what is the English plural of octopus?” – brings the discussion full circle. For this item at least, there seems to be no end to the usage debate, so I would like to know which form you prefer. Moreover, I am curious about whether you consider rhymes like those in O'Conner's usage guide a useful memory aid. Also, if you happen to know any other usage rhymes, please get in touch with me through the Bridging the Unbridgeable blog, at http://bridgingtheunbridgeable.com/english-today/, as your suggestions are very helpful for my study into the use of rhymes in giving usage advice.