Octopus has three acceptable pluralizations in English.

  Octopuses is correct by English rules.
  Octopodes is correct by strict etymological Greek-origin rules.
  Octopi is correct by English's pseudo-Latin cognate rules.

The latter means that any singular noun ending in a consonant and "-us" can be pluralized by chopping off the "-us" and appending an "-i" or "-ii", like alumnus, hippopotamus, virus, bacillus, hummus, lotus, oculus, cactus, and platypus. This has even been abused to facetiously pluralize similar-sounding endings, like Elvis or Winklevoss.

This is likely due to the many Anglophone schoolchildren subjected to Latin language lessons over the centuries who simply never cared about proper Latin grammar rules.

In the parking lot near my house, there are a bunch of Toyota Priuses that park in one corner. We've started calling them Prii.

why do robots group together in the dark?

Except there is no single authority of the English language (as seen in other language academies). As I mentioned in another comment, you may fall into a prescriptivist or descriptivist camp, but there's no authority to which one can appeal for a single answer.

Generally speaking, octopuses is preferred by most if not all well known dictionaries in modern usage, and the pseudo-Latin cognate has fallen out of favor. I don't think it's reflective of reality to argue that all three are equivalently correct.

Neither the prescriptivists nor the descriptivists are correct.

There is, in fact, a way to assume greater authority over the English language than the power wielded by the median speaker. The person who can inject a memorable phrase into the popular culture--whether by writing a line that is read by many, or by speaking one that is heard by many--can steer the language closer to the path they may prefer.

For all our quibbling over technical correctness, if an author or scriptwriter decides to keep "octopi" alive, all they have to do is write it, with no explanation or justification necessary.

Stam that in your rassoodock and let it digimmer. It could make you frumious or mimsy, but you will grok who the lords of language are.

The goal of descriptivists is to collect information about how words are being used currently and to compile a dictionary based on that information, so what you said about viral memes is compatible with descriptivism.

The best argument for prescriptivism has less to do with authority and more to do with people who have an interest in being able to communicate clearly. A better word than "prescriptivism" might be "subscriptivism". Presumably, we subscribe to the normal rules of the English language so that we mitigate miscommunication.

Purpose matters. The person who demands that everyone use "octopuses" is just an elitist asshole. The science institution, which demands that its members conform to a precise standard of language, is just doing its job.

A cromulent point indeed!

The style guides to most scientific journals will assert "octopuses", so you're unlikely to get "octopi" past that collective editorial authority, in any case - the others are however deemed acceptable alternates in common use.

... most scientific journals will assert "octopuses" ...

I saw a lecture by Peter Godfrey-Smith, the author of the book in TFA, and he also comes down on the side of "octopuses".

Honestly, as a native english speaker who is usually a nazi in spelling, grammar and pronunciation - octopi sounds most intuitively "correct" to me. Octopuses sounds awkward and inconsistent with idiomatic English, like a non-native speaker might guess at. Octopodes sounds like a scientific term.

As far as I'm concerned octopi is correct. Screw the etymology.

AFAIK (I'm not a native speaker), English language has short and long words. Short words are native, long words are foreign. It's because long words in other languages are composed: short root, and suffix(es) to make proper form. English language uses other rules, so remnants of foreign languages are not welcome, but foreign languages are associated with wisdom, so longer words are associated with wisdom and science too. Can you confirm that?

http://writing-skills.com/does-word-length-matter

English follows other languages into dark alleys, beats them senseless, then rifles through their pockets for loose vocabulary.

The various irregular forms and tenses of the existential verb, "to be", is etymologically stitched together from at least three distinct languages.

Remnants of foreign languages certainly are welcome, though they certainly get rough treatment in comparison to their language of origin. The majority of the whole corpus is "foreign", and a significant fraction of the 1000 most commonly used "core words" are from a different branch of the linguistic tree as the official branch for English.

This is, in large part, due to the Saxon and Norman invasions.

Pseudo-Greco-Latin words are associated with higher education, because for a long time, Latin was required for higher education at English-speaking universities. Thanks to the fact that such words can be composited from a variety of common Greek and Latin roots, it remains the etymological origin of choice for newly-coined words describing new scientific knowledge. English, of course, tosses their grammar onto the tire fire, and chops up the vocabulary like a butcher disassembles a side of beef.

Length is likely just a side effect of the etymological origins.

It's always difficult to produce hard and fast rules with English. But there are often two words (or stems) for things, one from the Germanic roots and one from Latin (either via Norman French, or from later scientific etc. addition) which leads us to see with our visual system. The older Germanic words tend to be for more commonplace vocabulary, whereas the Latin tends to be for more formal or technical usage (YMMV). But because the inputs to English are mostly indo-European these two roots are sometimes similar anyway.

It's more than difficult - it's impossible. The number of exceptions to every supposed rule in English is ridiculous. There is no way to learn the language except by absorption and rote.

That's sort of why I support octopi. It is predictable, idiomatic and consistent. You shouldn't have to research the origins of a word in order to pluralise it.

Octopie is a baked dish with eight lobes.

I don't know, could it also be because what became England was pretty romanised before the Saxon influence began in earnest?

Well the word Octopus was invented from the whole cloth by Linnaeus, presumably inspired by applying the prefix for eight, to the Ancient Greek work for an octopus which was "polypous"

I basically agree with you, but this also reflects where you are on the prescriptivist/descriptivist split.

https://en.wikipedia.org/wiki/Octopus#Etymology_and_pluraliz...

Anyway, while I wouldn't put it like you have, I agree with the bottom line -- spread the message of "octopuses"!

Nobody who's speaking Greek would say that either, as it's ancient Greek. Today, we say "octapodia", or, colloquially, "ctapodia".

Linguistically this is known as reanalysis.

According to James Bond it should be octopussies (or is it octopussys?).

Not quite:

https://youtu.be/wFyY2mK8pxk (Octopus - Merriam-Webster Ask the Editor)

You just can't win with grammar Nazis. If they'd written octopuses, someone would be in here telling them "It's octopi".

> grammar nazis

I think you mean "spelling nazis". ;)