Data Is or Data Are? Seven Grammar Questions Academic Style Guides Disagree On

If you have been told confidently that data is plural, and equally confidently that data is is now standard, both people were quoting a real authority. There is no single arbiter of academic English grammar, and on a handful of high-frequency questions the major style manuals give genuinely different rulings. This comparison sets out who says what, so you can make one decision, record it, and stop relitigating it every chapter.

The comparison at a glance

1. Data: the one that actually matters

Data is the Latin plural of datum. In the twentieth century that plural was compulsory in academic prose. In the twenty-first, general English has largely reanalysed it as a mass noun, like information or evidence, which takes a singular verb.

Both usages are now defensible in general writing. In a thesis, the deciding factor is your field:

• Psychology, education, health sciences and anything following APA 7: use the plural. The data were screened for outliers. These data suggest… APA is explicit, and markers in these fields will treat the singular as an error.
• Natural sciences and engineering: plural, almost universally, and datum retains a live singular meaning (a reference point in surveying and geodesy).
• Business, media studies, computing and much of the humanities: the singular mass-noun reading is normal and unremarkable — the data is stored in a relational database.

The rule that overrides all of this: whichever you choose, the pronouns and determiners must follow. The data were analysed and they showed… or The data was analysed and it showed… Mixing them inside one paragraph — the data is clear, and they suggest — is the only version that is unambiguously wrong.

2. Criteria, phenomena, analyses: the plurals nobody forgives

Unlike data, these have not been reanalysed and no authority permits the singular use:

• criterion (singular) → criteria (plural). One criteria is always an error.
• phenomenon → phenomena.
• analysis → analyses. Note the pronunciation difference, which is why this one survives spellcheckers.
• hypothesis → hypotheses. Thesis → theses.
• medium → media, except in the mass-communication sense, where the media is is widely accepted.

3. Uncountable nouns that have no plural at all

A different and more damaging error is pluralising an uncountable academic noun. Research, evidence, literature, information, feedback, advice, knowledge and equipment have no plural form in academic English.

So: previous research has shown, never previous researches; the literature suggests, never the literatures suggest; two pieces of evidence, never two evidences. This is one of the most recognisable markers of second-language academic writing, and it is one of the specific weaknesses addressed by the academic editing tools built for non-native English thesis writers.

The quantifier that goes with them

Uncountable nouns also select different quantifiers. Use much, little and amount with them — much of the evidence, a small amount of variance — and reserve many, few and number for countable nouns, as in many studies and a small number of participants. The commonest slip is a large amount of participants, which should be a large number of participants. The same test settles less versus fewer: less variance, but fewer cases.

4. Singular they

APA 7 endorses singular they both for a person who uses it and as a generic third-person pronoun, and explicitly discourages he or she constructions. Chicago accepts it for a named individual and has moved steadily towards accepting the generic use. UK academic publishing has been comfortable with it for years.

Practical position: use singular they for participants of unspecified gender. It is shorter, it is current, and it avoids the clumsy s/he that dates a thesis instantly. Where a participant’s pronouns are known, use them.

5. That versus which

This is the clearest transatlantic split. American style prescribes that for restrictive clauses and which, preceded by a comma, for non-restrictive ones:

• The instrument that we adapted showed acceptable reliability. (Restrictive — identifies which instrument.)
• The instrument, which we adapted from Osei (2024), showed acceptable reliability. (Non-restrictive — adds information.)

British academic usage accepts restrictive which without a comma: The instrument which we adapted… is perfectly standard in a UK thesis. What is never standard in either variety is the comma: a restrictive clause takes no commas, and a non-restrictive one takes them at both ends. That punctuation half of the rule is not optional, and it sits alongside the other meaning-changing marks in our list of punctuation rules examiners notice.

6. Split infinitives, and the other rules that are not rules

Three prohibitions that circulate in supervision but appear in no current style authority:

• Never split an infinitive. No manual forbids it. To adequately test the assumption is fine, and forcing the adverb elsewhere often changes the meaning.
• Never begin a sentence with and or but. Chicago calls this a widespread but baseless belief. Use it sparingly for emphasis; there is no rule against it.
• Never end a sentence with a preposition. An eighteenth-century transplant from Latin grammar. Rearranging to avoid it usually produces worse prose.

What is worth avoiding is not the construction but the reader’s reaction. If your supervisor holds one of these beliefs, comply in their chapters and move on — the argument costs more than the edit.

7. None, majority, number: agreement by sense

None is not a contraction of not one and takes either verb depending on sense: None of the participants was excluded (each one individually) or None of the participants were excluded (the group). Both are correct in every major authority.

Two related patterns are fixed rather than optional: a number of participants were (plural) but the number of participants was (singular); and the majority of responses were (plural, because the noun after of governs).

How to decide once and stop deciding

The cost of these questions is not the individual choice; it is the fifteen minutes you lose to each one, repeatedly, across nine months. Settle them in a single sitting:

1. Identify the style authority your department requires and check its ruling on data first.
2. Open a one-page style sheet at the front of your working file and write down each decision as you make it.
3. Add the language variety, the serial-comma decision and your capitalisation and hyphenation choices to the same page.
4. Re-read the sheet before you start each new chapter, and hand it to anyone who proofreads for you.

This is the same discipline that keeps British and American spelling from drifting across chapters, and it is worth ten minutes at the start of the project rather than four hours at the end.

The verdict

For most postgraduate theses in the social and health sciences: treat data as plural, keep criteria and phenomena plural without exception, use singular they, follow your language variety on which, and ignore the split-infinitive prohibition entirely. In business, computing and much of the humanities, the singular data is is equally defensible — but choose before chapter one, not after chapter five.

Two sentence-level decisions sit immediately next to these: which reporting verb to use when you introduce a source, and which tense each chapter takes. Together with agreement, they account for most of the surface-level comments an examiner will write in the margin.

Write it consistently from chapter one

Tesify holds one declared style across the whole document, so agreement, pronouns and variety stay consistent between the chapter you drafted in October and the one you finished in March.

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