Plurals That Trip Everyone Up: Potatoes, Analyses and the Rules

In June 1992, at a school in Trenton, New Jersey, the vice president of the United States watched a twelve-year-old write "potato" correctly on a blackboard and then encouraged him to add an e. The flash card he was working from was wrong, the boy was right, and the moment followed Dan Quayle for the rest of his career. It is remembered as a gaffe. It is also a fair measure of how shaky most of us feel about plurals once we step beyond "cats" and "dogs".

Most plurals are effortless. You add an s and move on. Then you meet "potato", "leaf", "city", "criterion" or "analysis", and a small doubt opens up. Leafs or leaves? Two analysis, two analysises, or something stranger?

The good news is that plurals are among the most orderly parts of English spelling. There are about half a dozen patterns, each with a reason, and a small museum of old forms that simply have to be known. This guide goes through them in the order you are likely to need them, with the logic that makes each one stick.

The default, and why it is cleverer than it looks

The basic rule is to add s: dog, dogs; idea, ideas; table, tables.

Now say "cats", "dogs" and "horses" aloud and listen to the endings. The first is an s sound, the second a z sound, and the third adds an entire extra syllable. Three different pronunciations, one spelling. That is not carelessness on the part of English. It is a deliberate economy: the s tells the reader "more than one" at a glance, whatever it sounds like. Linguists call a meaningful word part like this a morpheme, and English has a strong habit of keeping a morpheme's spelling constant even when its sound shifts. The past-tense "-ed" of "jumped", "played" and "wanted" works exactly the same way.

The plural is also one of the first spelling rules children discover for themselves. In a famous 1958 experiment, the psycholinguist Jean Berko showed young children a drawing of an invented creature, told them it was a "wug", then showed two and asked what they were. Children as young as four said "wugs", correctly pronounced with a z sound, for a word they had never heard. The rule was already in their heads. Writing it is a different matter: research by Terezinha Nunes and Peter Bryant shows that children first spell endings by sound, writing "kist" for "kissed", and only gradually learn that endings are spelled by meaning.

When the plural needs an extra syllable: -es

Add -es when a word ends in s, ss, x, z, ch or sh.

The reason is audible. Try to say "box" with a plain s attached, without adding a syllable. You cannot, or at least not in a way anyone would understand. English inserts a vowel to make the plural sayable, and the spelling follows the sound: boxes.

Two traps hide in that table. "Quiz" doubles its z to become "quizzes", following the same doubling rule that turns "hop" into "hopping" and protects the short vowel; our guide to the doubling rule explains it. And when ch is pronounced as k, there is no extra syllable, so you simply add s: stomachs, monarchs, epochs.

Potatoes and pianos

This is the one that catches the most people, including, famously, a vice president.

Start with the reliable part. If a vowel comes before the final o, add s: radios, zoos, videos, studios, patios. There are almost no exceptions.

When a consonant comes before the o, the words split into groups. A small set of old, everyday words take -es. The ones you are likely to need are potatoes, tomatoes, heroes, echoes, vetoes, torpedoes and embargoes. If you want a single scene to hold them together, try this: the heroes heard echoes of torpedoes over a lunch of potatoes and tomatoes. Veto and embargo you learn on their own.

Most other o-words take a plain s. That includes shortened words, like photos (from photograph), pianos (from pianoforte), memos and kilos; musical words from Italian, like solos, cellos and sopranos; and most recent borrowings, like logos and tacos. The shortened words make a kind of sense: the o is standing in for a longer word that has been cut off, and English treats it gently.

A third group goes both ways. Zeros and zeroes, mosquitoes and mosquitos, volcanoes and volcanos, tornadoes and tornados, mottoes and mottos are all accepted, and dictionaries differ over which they list first. Pick one and stay consistent.

Cities and days

For words ending in y, look at the letter before it.

After a consonant, change the y to i and add -es: city, cities; baby, babies; country, countries; story, stories. After a vowel, simply add s: day, days; key, keys; toy, toys; valley, valleys; attorney, attorneys.

The logic is visual. A y after a vowel is part of a vowel team (ay, ey, oy) and changing it would break the team apart. A y after a consonant is doing the work of a vowel on its own, so it can become an i without anything falling to pieces.

Two exceptions are worth knowing. Proper names keep their y, so you write the Kennedys, and you might meet two Marys at a party; changing the y would change the name. And a y after "qu" counts as following a consonant, because the u is really part of the consonant sound: soliloquy becomes soliloquies. The same y-to-i change reappears in happiness, carried and busier, so learning it here pays off well beyond plurals.

Leaves, but roofs

This is the plural rule people find most unfair, and it has the best story behind it.

In Old English, an f that fell between two vowels was pronounced as v. Old plurals ended in a vowel sound, so the f of a word like "leaf" found itself between vowels in the plural and was voiced. The pronunciation survived, and eventually the spelling caught up with it: leaves, loaves, wolves. The words in the right-hand column mostly have a different history. Chief and chef arrived later from French; cliff ends in a double f, which was never voiced; and roof and proof simply kept their f sound in most speech.

You can hear the old v in a set of noun and verb pairs that most people have never noticed. Belief, believe. Proof, prove. Grief, grieve. Half, halve. Shelf, shelve. The noun has the f, the verb has the v, and the ves plural is a cousin of the same old sound change.

A few words sit on the fence: scarves and scarfs, hooves and hoofs, dwarves and dwarfs are all accepted. The practical test is to say the plural aloud. If you hear a v, write ves. If you hear an f, write s.

Analyses, criteria, phenomena

Many academic and scientific words came into English from Latin and Greek and brought their original plurals with them. These are the plurals that trip up students, researchers and professionals most often, usually in writing that matters.

The first row is the one most people need. Every word ending in -sis forms its plural by changing -is to -es: analysis and analyses, diagnosis and diagnoses, hypothesis and hypotheses. Pronouncing the plural ending "-eez" helps fix it in memory.

"Criteria" and "phenomena" produce the classic error in the other direction: "a criteria", "this phenomena". The singulars are criterion and phenomenon. A quick check is to put "one" in front: if "one" fits, you need the -on form.

Several of these words now have an English plural as well, and both are correct. Formulas and formulae, antennas and antennae, indexes and indices, cactuses and cacti all appear in careful writing. Usage often splits by field: insects have antennae while radios have antennas, and books have indexes while mathematics has indices.

Watch for false Latin, too. "Octopus" is Greek, not Latin, so "octopi" rests on a mistake; dictionaries prefer "octopuses". "Virus" never had a Latin plural in use, so the only plural is "viruses". And "data", strictly the plural of "datum", is now widely treated as a mass noun in everyday and business writing ("the data is clear"), while many scientists still write "the data are". Both are accepted; consistency within a document is what readers notice.

The survivors from Old English

A handful of plurals change the vowel inside the word rather than adding anything. They are relics of an old sound change and there are only a few: man and men, woman and women, foot and feet, tooth and teeth, goose and geese, mouse and mice, louse and lice. Two more keep an old -en ending, ox and oxen, and child and children, which is in fact a double plural built up over centuries.

Some nouns do not change at all: sheep, deer, moose, aircraft, series and species are the same for one or many. "Fish" usually stays "fish", with "fishes" reserved for several different kinds.

These are genuine one-offs, and no new ones are being made. You already know almost all of them.

Traps that have nothing to do with the ending

Three errors show up constantly, even in the writing of good spellers.

The first is the apostrophe. A plural never takes one: apples, not "apple's"; the Smiths, not "the Smith's"; the 1990s, not "the 1990's". The one widely accepted exception is single lowercase letters, as in "mind your p's and q's", where "ps and qs" would be baffling.

The second is compounds, where the main noun takes the plural: mothers-in-law, attorneys general, passersby. Words ending in -ful simply add s at the end: spoonfuls, cupfuls.

The third is less a plural rule than a pile-up of s's. "Businesses" and "processes" defeat many people simply because of the number of sibilants in a row. Say the base word first, then add the syllable: business, businesses.

A ten-word self-test

Cover the answers and write the plural of each word from memory: box, tomato, radio, city, key, knife, chief, crisis, criterion, child.

The answers are boxes, tomatoes, radios, cities, keys, knives, chiefs, crises, criteria and children. Each one tests a different pattern. Box needs -es for the extra syllable. Tomato belongs to the small -es group, while radio has a vowel before its o. City changes y to i after a consonant; key keeps its y after a vowel. Knife voices its f; chief does not. Crisis follows the Greek -is to -es rule, criterion the -on to -a rule, and child is an Old English survivor.

Any you missed point you to the section worth rereading. Then, more importantly, test yourself again in two or three days, because recalling a word after a gap is what makes it stay.

The most useful thing to do next

Pick the pattern that catches you most often and learn it together with its reason. For many adults that is the Latin and Greek set; for children it is usually y to -ies and the o-words. A reason holds far better than a bare list.

Then practice by testing, not rereading. Cover the plural column in any table above, write the plurals from memory, check them, and repeat a few days later. That is the method memory research supports most strongly, and it is the one Spelling.School is built around. For the closely related question of what happens to a final e when you add an ending, see our guide to the drop-the-e rule, and for more words that trip people up, our list of commonly misspelled words.

Questions people ask

When do you add es to make a plural?

Add es when a word ends in s, ss, x, z, ch or sh, as in buses, classes, boxes, quizzes, churches and dishes. The extra letters reflect the extra syllable you hear when you say these plurals aloud. When ch is pronounced as k, as in stomach or monarch, you simply add s. A small group of words ending in a consonant plus o, such as potatoes and heroes, also take es.

Is it potatos or potatoes?

The correct spelling is potatoes, with an e. Tomatoes, heroes, echoes, vetoes and torpedoes follow the same pattern. Most other words ending in o simply add s, including pianos, photos, memos, solos and logos. When a vowel comes before the final o, as in radio or video, you always just add s.

What is the plural of analysis?

The plural of analysis is analyses. Words ending in sis come from Greek and form their plural by changing the is to es. The same pattern gives crises, theses, diagnoses, hypotheses and parentheses. The plural ending is usually pronounced like eez, which helps distinguish it from the singular in speech and in memory.

Why is it leaves but roofs?

In Old English, an f that fell between two vowels was pronounced as a v, so plurals such as leaves, loaves and wolves took on a v sound that later appeared in the spelling. Words such as roof, chief and belief either kept their f sound or entered English later, so they simply add s. A practical test is to say the plural aloud: if you hear a v, write ves, and if you hear an f, write s.

Is it criteria or criterion?

Criterion is the singular and criteria is the plural, so you write one criterion but several criteria. Phenomenon and phenomena follow the same Greek pattern. A common mistake is to write a criteria or this phenomena, mixing the plural form with a singular meaning. If the word one fits in front of it, you need the form ending in on.

Is data singular or plural?

Strictly, data is the plural of datum, and many scientists still write the data are. In everyday and business English, most writers now treat data as a mass noun, like information, and write the data is. Both uses are widely accepted by dictionaries and style guides. The important thing is to choose one and use it consistently within the same document.

Do you use an apostrophe to make a plural?

No. Plurals do not take an apostrophe, so you write apples, the Smiths and the 1990s. An apostrophe shows possession or a missing letter, not more than one. The one widely accepted exception is single lowercase letters, as in mind your p's and q's, where leaving out the apostrophe would make the letters hard to read.

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