Words Ending in -is: How to Make the Plural (Analysis → Analyses)
Quick Answer
Words that end in -is change the i to an e: one analysis, two analyses. These words come from Greek and appear a lot in school, university and news writing.
See the Pattern First
Read these sentences. Look at the endings in blue.
- One crisis is bad. Two crises are worse.
- The doctor made a diagnosis. She makes many diagnoses every day.
- This is my thesis. The library keeps thousands of theses.
- Write one hypothesis. Test both hypotheses.
The spelling barely changes — only the i becomes an e. But the sound changes a lot: “crisis” ends in a hissing -sis, and “crises” ends in -seez. Say them out loud once; your ear will remember it faster than your eye.
The Full List — 14 Words That Follow This Rule
Learn these as one group. Once you hear the -seez ending, every word below follows.
| One | Many | One | Many |
|---|---|---|---|
| analysis | analyses | axis | axes |
| basis | bases | crisis | crises |
| diagnosis | diagnoses | ellipsis | ellipses |
| hypothesis | hypotheses | nemesis | nemeses |
| paralysis | paralyses | parenthesis | parentheses |
| synopsis | synopses | synthesis | syntheses |
| thesis | theses | oasis | oases |
One of these is asked about far more than the rest, so it has its own full lesson: the plural of oasis.
Why These Words Are Different
These words came into English from Greek, and English kept the Greek plural instead of adding -s. That is why “analysises” sounds so wrong — English never built that form.
Here is the useful part: almost every -is word in this group is an academic or medical word. If you meet a new word ending in -is in a textbook, you can predict its plural with confidence. That is a real shortcut.
-is becomes -es. Say it “-seez”.
One Word That Trips Everyone Up
Axes is two words in one, and only the sound tells them apart:
- axis → axes (said AX-eez) — the lines on a graph.
- axe → axes (said AX-iz) — the tool for cutting wood.
They are spelled the same. Only context and sound separate them, so do not panic if you see “axes” and it does not mean graphs.
Mistakes Learners Make (You Are Not Alone)
These three appear in student writing constantly. Spotting them now saves you marks later.
- ✗ two analysises → ✓ two analyses
- ✗ many crisises → ✓ many crises
- ✗ the parenthesis are → ✓ the parentheses are (one parenthesis, two parentheses — the brackets come in a pair)
If you have written one of these, you are in very good company — these are among the most-corrected words in university writing.
Your Turn — Quick Quiz
Five questions. Take your time — the table above is still there if you need it.
1. 1. The scientist tested three different ____.
2. 2. The country survived two economic ____ in ten years.
3. 3. Put the extra information inside ____.
4. 4. Which is the plural of “diagnosis”?
5. 5. The graph has two ____: one going across, one going up.
Keep Going
You just learned 14 words with one rule. Better still, you can now predict the plural of an -is word you have never seen before.
But English borrowed from Latin too, not just Greek — and those words behave differently. One cactus, two cacti? Or two cactuses? Both are used, and there is a reason.
Next lesson: Latin words ending in -us: cactus, focus, virus
Sources
I’m Khamis Maiouf. English is not my first language – I learned it as an adult in the UK, passed Functional Skills Level 2 in English, qualified in Hairdressing at Level 3, and I’m now studying Business at university. For over five years I’ve taught ESOL classes in my community and tutored students through GCSE English. I write every lesson on this site myself, for the learner I used to be.
