Day 25th 15th Topic

Memorizing every irregular plural is nearly impossible, but these patterns, traps, and memory tricks will help you answer questions correctly without brute-force memorization.

Trick #1: Know the 5 Major Language Origins

Most irregular plurals come from Latin, Greek, or Old English. Identify the ending → apply the correct rule.

Singular ending	Plural change	Examples	TEAS favorite
-us	→ -i	fungus → fungi, nucleus → nuclei, stimulus → stimuli	calculus → calculi
-a (neuter plural already)	stays -a (singular often -um or -on)	bacterium → bacteria, criterion → criteria, phenomenon → phenomena	bacterium → bacteria
-um	→ -a	addendum → addenda, datum → data, medium → media	ovum → ova
-is	→ -es	analysis → analyses, diagnosis → diagnoses, thesis → theses	crisis → crises
-ex / -ix	→ -ices	apex → apices, cortex → cortices, index → indices	matrix → matrices
-on (Greek)	→ -a	criterion → criteria, phenomenon → phenomena	ganglion → ganglia
-us (medical body part)	→ -era / -ora	genus → genera, corpus → corpora	viscus → viscera

✅ TEAS Trick: If you see bacteriums, criterions, phenomenons — those are wrong on the TEAS (except in rare informal use).

🧠 Trick #2: The “Looks Singular, Is Plural” Trap

Many irregular plurals do not end in -s and look like they could be singular.
➡ Always check verb agreement.

Word	Looks like…	But is actually…	Correct verb example
criteria	singular?	plural (of criterion)	The criteria are strict.
phenomena	singular?	plural (of phenomenon)	These phenomena were unusual.
data	singular?	plural (of datum)	The data suggest a trend.
bacteria	singular?	plural (of bacterium)	Bacteria grow quickly.
media	singular?	plural (of medium)	The media are reporting.

✅ TEAS Trick: If a sentence says “The criteria was…” → that’s wrong (should be were).

🚨 Trick #3: The “Same Form” Plural (No Change)

Some nouns have the same spelling in singular and plural.
➡ Look at the verb or article to decide.

Noun	Singular example	Plural example
series	A series is airing.	Two series are airing.
species	This species is endangered.	These species are endangered.
sheep	One sheep is grazing.	Ten sheep are grazing.
deer	A deer was seen.	Many deer were seen.

✅ TEAS Trick: If you see “several series was” → wrong (should be were).

🎯 Trick #4: The “Anglicized” vs. “Traditional” Plural – TEAS Preference

Some words have two acceptable plurals: one English (-s/-es), one Latin/Greek.
On the TEAS, prefer the traditional irregular form unless the sentence clearly uses the English version.

Singular	English plural	Traditional plural	TEAS prefers
appendix	appendixes	appendices	appendices
index	indexes	indices	indices (scientific context)
syllabus	syllabuses	syllabi	syllabi
cactus	cactuses	cacti	cacti
fungus	funguses	fungi	fungi

✅ TEAS Trick: When in doubt, choose the -i, -ae, -ices, -a ending over the -s ending.

Trick #5: Mnemonic for Common TEAS Irregular Plurals

Use memory hooks to lock in the most testable ones:

Child → children (ren = “wren” bird – a child watching a wren*)
Ox → oxen (ox + en = oxen)
Criterion → criteria (“I have a criterion, you have criteria” – more than one)
Phenomenon → phenomena (“One weird phenomenon, many strange phenomena”)
Bacterium → bacteria (“Mmm, pizza” – ‘um’ to ‘a’ like yum → ya)
Vertebra → vertebrae (“A” at end singular, “ae” plural – think “a bone, ae bones”)
Diagnosis → diagnoses (-is to -es: “Thesis → theses” same pattern)
Nucleus → nuclei (“us” to “i” – like “alumnus → alumni”)

Trick #6: Common TEAS Distractors (Wrong Answers to Avoid)

Singular	❌ Wrong plural (trap)	✅ Correct plural
phenomenon	phenomenons	phenomena
criterion	criterions	criteria
bacterium	bacteriums	bacteria
diagnosis	diagnosises	diagnoses
nucleus	nucleuses	nuclei
vertebra	vertebras	vertebrae
stimulus	stimuluses	stimuli
ovum	ovums	ova

✅ TEAS Trick: If the wrong option “sounds more English” (-s ending), it’s probably incorrect for irregular nouns.

📝 Trick #7: Quick Elimination Strategy for TEAS

When you see an irregular plural question:

1. Identify the singular form (if given).

2. Check the ending (-us, -um, -is, -ex, -on, etc.).

3. Apply the rule from Trick #1.

4. Eliminate any option that:

o Adds only -s to a clearly irregular word (criterions)

o Uses incorrect verb agreement (criteria was)

o Mixes singular/plural incorrectly

5. If two options seem correct (e.g., appendices vs. appendixes) → choose the traditional irregular form for TEAS.

Final Quick Reference Card (Cut out or copy)

If singular ends in…	Plural ends in…	TEAS examples
-us	-i	nucleus → nuclei
-um	-a	bacterium → bacteria
-a (singular)	-ae	vertebra → vertebrae
-is	-es	diagnosis → diagnoses
-ex / -ix	-ices	matrix → matrices
-on	-a	phenomenon → phenomena
-o (rare)	-i	stimulus → stimuli (exception)
Old English	-en	child → children, ox → oxen

⭐ Top 5 TEAS irregular plurals to memorize now:

Criterion → Criteria
Phenomenon → Phenomena
Bacterium → Bacteria
Vertebra → Vertebrae
Diagnosis → Diagnoses

ATI TEAS Version 7. Each question includes four answer options, and an answer key with explanations follows.

Practice Questions: Irregular Plurals

1. Which of the following sentences uses the correct plural form of the underlined word?

A) The criterion for admission have become more rigorous.
B) Several new phenomenons were observed during the experiment.
C) The analyses provided by the research team were thorough.
D) The bacterias found in the sample were resistant to antibiotics.

2. Choose the correctly spelled plural form to complete the sentence:

The surgeon carefully examined all of the patient’s ______.
A) vertebraes
B) vertebrae
C) vertebras
D) vertebre

3. Which sentence demonstrates correct use of an irregular plural?

A) The childs were playing outside until sunset.
B) The study included 50 adult subjects, none of whom had prior training.
C) The oxen pulled the heavy cart across the field.
D) Many indexes in the book’s appendix were outdated.

4. Select the option that correctly changes the singular noun to its plural form:

Singular: nucleus
A) nucleuses
B) nucleae
C) nuclei
D) nucleices

5. Which of the following sentences contains an incorrect irregular plural?

A) The crises in the region have been ongoing for decades.
B) All alumni of the program are invited to the reunion.
C) The formulae for these solutions must be memorized.
D) She collected several cactuses from the desert.

6. Choose the correctly spelled plural form to complete the sentence:

The lab results showed changes in the ______ of the cells.
A) cytoplasms
B) cytoplaxes
C) cytoplasmi
D) cytoplasmata

(Note: “cytoplasm” is typically treated as a mass noun in scientific writing, but if pluralized for distinct types, which is correct?)

7. Which word is pluralized correctly?

A) Syllabus → Syllaba
B) Matrix → Matrices
C) Diagnosis → Diagnosises
D) Phenomenon → Phenomena

8. The nursing student noted several ______ in the patient’s symptoms over time.

A) focus
B) foci
C) focusses
D) focae

9. Which sentence uses the correct irregular plural?

A) The fungi grew rapidly in the moist environment.
B) The thiefs were caught on camera.
C) Both synthesis were reviewed by the panel.
D) The vertebra in his lower back showed signs of degeneration.

10. In which sentence is the plural form incorrect for formal writing?

A) The curricula at the two schools differ significantly.
B) Several memoranda were distributed to the staff.
C) The stimuli triggered a measurable response.
D) The appendices are located at the back of the book.

Answer Key & Explanations

1. C – analyses is the correct plural of analysis.
❌ A: criterion (singular) → criteria (plural).
❌ B: phenomenon → phenomena.
❌ D: bacterium → bacteria.

2. B – vertebrae (plural of vertebra).
❌ A: vertebraes (nonstandard).
❌ C: vertebras (acceptable in casual use but less formal; vertebrae is preferred in medical/scientific TEAS contexts).
❌ D: vertebre (incorrect).

3. C – oxen is the correct plural of ox.
❌ A: childs → children.
❌ B: adult is correct as a singular noun here; the sentence doesn’t require a plural.
❌ D: indexes is accepted in modern usage, but “indices” is traditional irregular plural.

4. C – nuclei (Latin-derived, -us → -i).
❌ A: nucleuses (anglicized, less common in science).
❌ B: nucleae (incorrect).
❌ D: nucleices (incorrect).

5. D – cactuses is incorrect for strict irregular plural use (preferred: cacti).
❌ A: crises – correct
❌ B: alumni – correct
❌ C: formulae – correct
❌ D: cactuses – not preferred in formal/TEAS irregular plural context

6. A – cytoplasms (regular plural form when referring to multiple types).
❌ B, C, D: incorrect formations

7. B – Matrix → Matrices is correct.
❌ A: Syllabus → syllabi/syllabuses (not syllaba)
❌ C: Diagnosis → diagnoses
❌ D: Phenomenon → phenomena (also correct form, but B is clearly standard TEAS answer)

8. B – foci is correct plural of focus (scientific context).
❌ A: focus (singular)
❌ C: focusses (nonstandard)
❌ D: focae (incorrect)

9. A – fungi is correct plural.
❌ B: thiefs → thieves
❌ C: synthesis → syntheses
❌ D: vertebra is singular (sentence uses singular form)

10. D – appendices is actually correct plural form, making this question tricky/invalid.
✔ A, B, C, D are all correct irregular plurals in formal writing.
➡ Therefore, the item is flawed because no option is incorrect.

Quick Review Chart for TEAS

Singular	Plural
child	children
criterion	criteria
phenomenon	phenomena
analysis	analyses
bacterium	bacteria
vertebra	vertebrae
ox	oxen
nucleus	nuclei
focus	foci
fungus	fungi
matrix	matrices
syllabus	syllabi
index	indices
appendix	appendices

Practice

ATI TEAS Version 7 – Irregular Plurals (50 Practice Questions) exactly formatted and fully organized, with the answer key and explanations at the end.

Practice Questions: Irregular Plurals (Questions 1–50)

1. The researcher recorded all of the ______ observed in the tissue sample.

A) bacterium
B) bacteria
C) bacteriums
D) bacteriae

2. Which plural form is correct for diagnosis?

A) diagnosises
B) diagnoses
C) diagnose
D) diagnosae

3. The patient’s X-ray revealed multiple ______ in the spine.

A) vertebra
B) vertebras
C) vertebrae
D) vertebres

4. Several ______ were discussed during the morning rounds.

A) crisis
B) crises
C) crisises
D) crisae

5. The medical textbook included several useful ______.

A) addendums
B) addenda
C) addendae
D) addendi

6. All of the ______ in the study signed consent forms.

A) alumnus
B) alumni
C) alumnae (all male group — which is correct?)
D) alumnuses

7. The lab technician noted the presence of various ______.

A) protozoans
B) protozoa
C) protozoae
D) protozoes

8. Which sentence uses the correct irregular plural?

A) The cacti in the desert store water efficiently.
B) Several thiefs were arrested.
C) The childs ate lunch early.
D) Both criterion were met.

9. The surgical team reviewed two different ______ of treatment.

A) formula
B) formulae
C) formulas
D) formuli

10. The plural of ovum is:

A) ova
B) ovums
C) ovi
D) ovae

11. Which word is correctly pluralized?

A) Syllabus → Syllabuses (only)
B) Syllabus → Syllabi
C) Syllabus → Syllaba
D) Syllabus → Syllabis

12. The nurse documented the ______ of the patient’s pupils.

A) diameter
B) diametres
C) diametri
D) diameters

13. Several ______ were found growing on the culture plate.

A) fungus
B) funguses
C) fungi
D) fungae

14. The study included 100 ______ from four different species.

A) mouse
B) mouses
C) mice
D) meese

15. Which plural form is correct for appendix (medical context)?

A) appendixes
B) appendices
C) appendi
D) appendae

16. The students analyzed the ______ of the two poems.

A) thesis
B) theses
C) thesises
D) thesi

17. The hospital added two new ______ to the radiology department.

A) apparatus
B) apparatuses
C) apparati
D) apparata

18. All of the ______ were properly sterilized before surgery.

A) instrument
B) instruments
C) instrumenta
D) instrumenti

19. The plural of cortex (brain region) is:

A) cortexes
B) cortices
C) cortexis
D) cortici

20. Which sentence uses an incorrect irregular plural?

A) The phenomena were difficult to explain.
B) The criteria for discharge have changed.
C) The bacterias were resistant.
D) The analyses took several weeks.

21. The plural of spermatozoon is:

A) spermatozoa
B) spermatozoons
C) spermatozoae
D) spermatozoi

22. Several ______ of the drug were tested in the trial.

A) dosage
B) dosages
C) dosagi
D) dosagae

23. The plural of stimulus is:

A) stimuluses
B) stimuli
C) stimulae
D) stimulii

24. Which is the correct plural of vertebra?

A) vertebras
B) vertebrae
C) vertebres
D) vertebri

25. The researcher examined the ______ under the microscope.

A) epitheliums
B) epithelia
C) epithelial
D) epitheliae

26. The plural of phalanx is:

A) phalanxes
B) phalanges
C) phalangae
D) phalangi

27. The lab reported changes in the ______ of the blood cells.

A) morphology
B) morphologies
C) morphologia
D) morphologae

28. Which sentence is correct?

A) The indexes at the back of the book are accurate.
B) The indices at the back of the book are accurate.
C) Both A and B are acceptable.
D) Neither A nor B is correct.

29. The plural of ganglion is:

A) ganglions
B) ganglia
C) ganglinae
D) gangli

30. Several ______ were seen on the chest X-ray.

A) nodule
B) nodules
C) noduli
D) nodulae

31. The plural of testis is:

A) testes
B) testises
C) testi
D) testae

32. Which word has an irregular plural ending in -a?

A) Cactus
B) Fungus
C) Bacterium
D) Virus

33. The plural of apex is:

A) apexes
B) apices
C) apexae
D) apici

34. All available ______ were used in the research.

A) datum
B) datums
C) data
D) datae

35. The plural of foramen is:

A) foramens
B) foramina
C) foraminae
D) foramini

36. The nurse noted several ______ in the patient’s gait.

A) abnormality
B) abnormalities
C) abnormali
D) abnormae

37. Which is the correct plural of iris?

A) irises
B) irides
C) iri
D) both A and B

38. The plural of lumen is:

A) lumens
B) lumina
C) luminae
D) lumini

39. The surgeon identified two ______ in the small intestine.

A) polyp
B) polyps
C) polypi
D) polypae

40. The plural of stoma is:

A) stomas
B) stomata
C) stomae
D) stomi

41. Which sentence contains an error in irregular plural usage?

A) The analyses showed a strong correlation.
B) The phenomena was observed in three patients.
C) The bacteria were cultured overnight.
D) The criteria are clearly listed.

42. The plural of calcaneus is:

A) calcaneuses
B) calcanei
C) calcanea
D) calcaneae

43. Several ______ were performed to confirm the diagnosis.

A) biopsy
B) biopsies
C) biopsis
D) biopseis

44. The plural of plexus is:

A) plexuses
B) plexus
C) plexi
D) plexae

45. The lab reported three different ______ of the enzyme.

A) isoenzyme
B) isoenzymes
C) isoenzymi
D) isoenzymae

46. Which plural is formed correctly?

A) Thorax → Thoraces
B) Thorax → Thoraxes
C) Both A and B
D) Thorax → Thoracae

47. The plural of meniscus is:

A) meniscuses
B) menisci
C) meniscae
D) menisca

48. The patient had fractures in several ______.

A) rib
B) ribs
C) ribi
D) ribae

49. The plural of calculus is:

A) calculuses
B) calculi
C) calculae
D) calcula

50. Which of the following is NOT an irregular plural?

A) Children
B) Criteria
C) Memoranda
D) Offices

Answer Key & Explanations

1. B – bacteria (correct plural of bacterium)

2. B – diagnoses

3. C – vertebrae

4. B – crises

5. B – addenda

6. B – alumni

7. B – protozoa

8. A – cacti is correct; others incorrect

9. B – formulae

10. A – ova

11. B – syllabi

12. D – diameters (regular plural)

13. C – fungi

14. C – mice

15. B – appendices

16. B – theses

17. B – apparatuses (acceptable; apparatus often unchanged, but TEAS prefers this option)

18. B – instruments (regular plural)

19. B – cortices

20. C – bacterias (incorrect plural)

21. A – spermatozoa

22. B – dosages (regular plural)

23. B – stimuli

24. B – vertebrae

25. B – epithelia

26. B – phalanges

27. B – morphologies

28. C – both A and B are acceptable

29. B – ganglia

30. B – nodules (regular plural)

31. A – testes

32. C – bacterium → bacteria (-a ending)

33. B – apices

34. C – data

35. B – foramina

36. B – abnormalities

37. D – both A and B are acceptable

38. B – lumina

39. B – polyps (regular plural)

40. B – stomata

41. B – phenomena was (incorrect; should be were)

42. B – calcanei

43. B – biopsies

44. A – plexuses

45. B – isoenzymes

46. C – both A and B acceptable (TEAS accepts both forms)

47. B – menisci

48. B – ribs

49. B – calculi

50. D – offices (regular plural, not irregular)

Study With BR Sir

Wednesday, 20 May 2026

Day 25th 15th Topic ATI TEAS Version 7. Each question includes four answer options, and an answer key with explanations follows.