Creating plural nouns in English is bewildering, and not just to those who come to it from another tongue. Between the ablaut, or mutated plurals, of foot and feet, goose and geese, and words from Latin and Greek such as index and indices, octopus and octopi, not to mention alumna, alumnus, alumnae, and alumni, there seem to be no rules and a welter of confusion. What's the key?

Well, the answer is that there actually is a welter of confusion about English plurals. Consider the following:

index / indexes / indices
appendix / appendixes / appendices
the Wilkins / the Wilkinses
sheep / sheep
shrimp / shrimp / shrimps

All of these are correct, in one context or another. What's a grammar gal or guy to do?

The formation of regular English plurals does follow some general rules, but even those seem to devolve into chaos pretty quickly.

One of the best brief introductions to the topic is on Wikipedia, which moves succinctly and clearly through a discussion of regular plurals formed by adding morpheme suffixes (i.e. is, -ies, etc.) according to understandable rules.

And just as swiftly we are looking at conflicting exceptions such as Two Germanies or Two Germanys and how there are always Two Sicilies, not Sicilys but never any Harries.

Note the "how," not the "why" in the previous sentence. There doesn't seem to be an easy answer as to why some plurals are formed one way or another. And so very often, the "correct" plural depends on context. A doctor removes appendixes; an editor adds appendices.

As ever, I advise that the best way to proceed is to choose a standard - a dictionary or well-regarded style guide - and abide by those rules within a publishing house, book, publication, article, or other circumscribed piece of writing. Pick your arena, decide on the rule book, and play ball!