English has borrowed heavily from ancient Latin, Greek, and foreign languages. In formal, academic, scientific, and legal contexts, many foreign loanwords retain their original classical plural forms rather than adopting the standard English -s or -es suffix. Mastering these irregular classical plurals is essential for competitive examinations (GRE, GMAT, IELTS, UPSC) and academic publishing.

The Core Rule

Foreign loanwords from Latin and Greek follow specific singular-to-plural termination transformations based on their original declensions (e.g., -is → -es, -um → -a, -on → -a, -us → -i). Ensure that the verb agreement matches the Latin/Greek plural form.

Key Examples

✅ Latin -um → -a: The historical stratum is deep → Multiple historical strata are visible.
✅ Greek -is → -es: The economic crisis is severe → Multiple global crises are emerging.
✅ Greek -on → -a: A natural phenomenon was observed → Rare natural phenomena were observed.

1. Categorized Latin & Greek Plural Rules

Here are the primary classical termination rules and their standard singular/plural pairs:

Latin and Greek Pluralization Patterns
Termination PatternSingular FormClassical Plural FormExample Sentence
-is → -es (Greek)crisis, oasis, thesis, hypothesis, analysiscrises, oases, theses, hypotheses, analyses"All three doctoral theses were approved."
-um → -a (Latin)datum, medium, stratum, bacterium, erratumdata, media, strata, bacteria, errata"These financial data indicate strong growth."
-on → -a (Greek)criterion, phenomenon, automatoncriteria, phenomena, automata"What are the principal criteria for selection?"
-us → -i (Latin)alumnus, syllabus, stimulus, nucleus, locusalumni, syllabi, stimuli, nuclei, loci"The university alumni were invited."
-a → -ae (Latin)formula, alumna, larva, antenna, nebulaformulae, alumnae, larvae, antennae, nebulae"The chemical formulae were verified."
-ix / -ex → -ices (Latin)appendix, index, matrix, vertexappendices, indices, matrices, vertices"Refer to the indices at the end of the report."

2. Modern Shift: Classical vs. Anglicized Plurals

In modern informal English, some classical loanwords have developed standard Anglicized plurals ending in -s. However, academic writing strictly demands the classical form:

  • Syllabus: Syllabi (formal academic) vs Syllabuses (informal).
  • Formula: Formulae (scientific context) vs Formulas (general context).
  • Index: Indices (financial/mathematical) vs Indexes (book pages).
  • Appendix: Appendices (book documents) vs Appendixes (medical organs).
Exam Trap: Data, Criteria, & Media

In formal academic English, data, criteria, media, phenomena are plural and require plural verbs (e.g., "The data show...", "These criteria are met"). Using singular verbs with data or criteria is one of the most frequent error-spotting questions in UPSC, SSC, and GMAT exams.

3. Common Errors and Corrections

Correct vs. Incorrect Usage
❌ Incorrect Usage✅ Correct Usage
This criteria is not applicable to our project.This criterion is not applicable to our project.
The economic crisises affected several nations.The economic crises affected several nations.
The data collected by the research team is inconclusive.The data collected by the research team are inconclusive. (Formal academic)

✍️ Quick Practice — Test Your Knowledge

Provide the correct classical plural form for each singular noun:

  1. Hypothesis → ____________
  2. Phenomenon → ____________
  3. Alumnus (male graduate) → ____________

Answers: 1. Hypotheses  |  2. Phenomena  |  3. Alumni

Summary & Key Takeaways

  • Memorize Greek/Latin termination shifts: -is → -es, -um → -a, -on → -a, -us → -i.
  • Treat criteria, phenomena, data, strata as plural nouns requiring plural verbs in formal writing.
  • Use classical plurals (formulae, indices, appendices) for scientific and academic registers.