Leaf or Leafs? Plural of words ending in -f/-fe

During the Polish national exams in May 2026, one of the grammar tasks sparked an avalanche of comments online. It was about a seemingly simple thing: forming the plural of the word leaf.

Many students automatically added the -s ending, creating the incorrect leafs.

If you also find yourself hesitating over the plural of words like leaf, knife, or shelf, this article is for you. We will explain the simple phonetic rule behind this change and sort out the exceptions once and for all.

Why is "leafs" a mistake? The Rule of Voicing

In English, most nouns form their plural by adding an -s or -es ending (e.g., dog -> dogs, box -> boxes). However, there is a group of words ending in -f or -fe where both spelling and pronunciation change:

The Rule: The -f or -fe ending changes to -ves in the plural.

Why does this happen? The answer lies in the biology of our speech organs.

The /f/ sound is voiceless (we don't use our vocal cords). When we add the plural ending to it, our speech apparatus tries to make the job easier. Transitioning from the voiceless /f/ to the voiced /z/ (which we hear in the -s ending) is physically difficult. Therefore, the English language paved an easier path: the voiceless /f/ changes into a voiced /v/, and the spelling reflects this by adding -ves.

10 Most Common Words You Need to Remember

Here is a list of the ten most important nouns that follow this rule. These are the ones that appear most frequently on tests and in everyday business communication:

• leaf ──► leaves
• thief ──► thieves
• knife ──► knives
• wife ──► wives
• shelf ──► shelves
• half ──► halves
• life ──► lives
• wolf ──► wolves
• loaf ──► loaves
• calf ──► calves

Examples in sentences:

• The autumn leaves are falling from the trees.
• Put the books back on the shelves, please.
• We cut the apple into two halves.

Watch Out for "False Exceptions" (when it stays as -s)

Not every word ending in -f changes to -ves. There is a group of words (often newer or borrowed from other languages) where the /f/ pronunciation has become so established that we simply add a regular -s ending:

• roof -> roofs (Never: rooves)
• cliff -> cliffs
• chef -> chefs (Never: cheves)
• belief -> beliefs
• safe -> safes (Note: save is a verb meaning "to rescue/store"!)

Quick Test: Check Your Knowledge!

Choose the correct plural form for the highlighted words:

1. We bought three (loafs / loaves) of fresh bread.

   • Correct answer: loaves (bread loaves follow the rule of changing to -ves).

2. The police caught the (thiefs / thieves) yesterday.

   • Correct answer: thieves (thieves – written with -ves).

3. Many houses in Poland have flat (roofs / rooves).

   • Correct answer: roofs (roof is an exception, we only add -s).

4. Be careful, these (knifes / knives) are very sharp!

   • Correct answer: knives (knives – the -fe ending changes to -ves).

Summary

Words ending in -f/-fe usually change their ending to -ves in the plural (e.g., leaf -> leaves). This happens for phonetic reasons – it is easier for us to pronounce a voiced /v/ than a voiceless /f/ before a plural ending. You simply have to memorize exceptions like roofs, chefs, or cliffs.

Want to master these rules in practice instead of just reading about them? In my Executive English sessions, we do real business simulations and pull mistakes out by their roots.