Traditional rule: "each other" for TWO people; "one another" for THREE OR MORE. In modern English many natives use them interchangeably, but formal English maintains the distinction.
EACH OTHER: reciprocal pronoun indicating a mutual action — each one performs it toward the other. Traditional use: when there are TWO people or entities. "John and Maria helped each other" = John helped Maria and Maria helped John (two people, mutual action). EACH OTHER can take a possessive: "They borrowed each other's notes." As direct object: "They called each other." As indirect object: "They wrote to each other." As possessive: "They know each other's weaknesses." In CONTEMPORARY informal English, EACH OTHER and ONE ANOTHER are frequently used interchangeably, and many modern style guides no longer insist on the distinction.
The two divisions had rarely communicated with each other directly before the restructuring — most coordination had gone through the executive layer.
The co-founders complement each other well — one brings deep technical expertise while the other has a strong commercial and client-facing background.
The two negotiating teams had not met face to face before the summit, though they had corresponded with each other extensively over the previous three months.
ONE ANOTHER: reciprocal pronoun with the same meaning as EACH OTHER, traditionally used when there are THREE OR MORE people or entities. "The five team members supported one another throughout the project." ONE ANOTHER can take a possessive: "They shared one another's resources." In practice, the two/three+ distinction has weakened in modern English. ONE ANOTHER sounds slightly more formal and literary than EACH OTHER. Both are INCORRECT with intransitive verbs that do not take a reciprocal complement: you cannot say "they slept each other" or "they arrived one another."
The departments had historically operated in silos, rarely sharing information with one another, which had led to duplicated efforts and missed opportunities.
In high-performing teams, members consistently challenge one another's assumptions in a way that generates better ideas rather than defensiveness.
The four regional offices had developed distinct cultures over the years and needed structured opportunities to learn from one another's best practices.
Common mistake
Classic errors: (1) Using THEMSELVES where EACH OTHER should go: "They praised themselves" = they praised their own selves (each one praised themselves, not mutually). "They praised each other" = they praised each other mutually (A praised B and B praised A). REFLEXIVE (themselves) = the action returns to the subject. RECIPROCAL (each other) = the action goes from one to another. (2) "Each others" = INCORRECT. The possessive is always "each other's" (apostrophe before s): "each other's opinions." (3) "One anothers" = INCORRECT. The possessive is "one another's": "one another's work." (4) "They met themselves" = INCORRECT for mutual meeting. Correct: "They met each other" or simply "They met."
Trick to remember it
The REFLEXIVE vs RECIPROCAL TEST: replace the phrase with "A did X to B, and B did X to A." If it makes sense = EACH OTHER / ONE ANOTHER (reciprocal). If the sentence means "A did X to themselves and B did X to themselves" = REFLEXIVE (themselves/himself/herself). "They helped each other" = A helped B, and B helped A (reciprocal). "They helped themselves" = A helped themselves, and B helped themselves (reflexive). Number rule: TWO = each other (traditional). THREE OR MORE = one another (traditional). MODERN: interchangeable in many contexts. When in doubt in formal writing, apply the traditional rule.
Quick rule
Each other = mutual action between TWO (traditional rule). One another = mutual action between THREE OR MORE (traditional rule). In modern English: interchangeable. Never "each others" — always "each other's" (possessive). Reflexive (themselves) is not the same as reciprocal (each other).
Did you know?
The rule "each other for two, one another for three or more" is a perfect example of a prescriptive norm with no solid historical basis. Linguists have shown that canonical writers like Shakespeare and other classic English authors used both forms interchangeably, without respecting a systematic numerical distinction. The rule was codified by 18th and 19th century grammarians who tried to "regularize" English artificially. Today, linguist David Crystal and other contemporary experts classify this distinction as "one of the grammatical rules taught without real historical basis." Most native English speakers do not apply it in natural speech, and many modern style guides (including the Chicago Manual of Style since 2010) no longer prescribe it as mandatory.
Exercise 1 · Pick the right one
After the merger, the two companies needed time to understand _____ organizational cultures before attempting to integrate their HR systems.
Exercise 2 · Pick the right one
The six regional directors had never been in the same room before and needed the retreat to finally introduce _____ and establish working relationships.
Exercise 3 · Form the word
Each other = mutual action between TWO (traditional rule). One another = mutual action between THREE OR MORE (traditional rule). In modern English: interchangeable. Never "each others" — always "each other's" (possessive). Reflexive (themselves) is not the same as reciprocal (each other).
Classic errors: (1) Using THEMSELVES where EACH OTHER should go: "They praised themselves" = they praised their own selves (each one praised themselves, not mutually). "They praised each other" = they praised each other mutually (A praised B and B praised A). REFLEXIVE (themselves) = the action returns to the subject. RECIPROCAL (each other) = the action goes from one to another. (2) "Each others" = INCORRECT. The possessive is always "each other's" (apostrophe before s): "each other's opinions." (3) "One anothers" = INCORRECT. The possessive is "one another's": "one another's work." (4) "They met themselves" = INCORRECT for mutual meeting. Correct: "They met each other" or simply "They met."
The REFLEXIVE vs RECIPROCAL TEST: replace the phrase with "A did X to B, and B did X to A." If it makes sense = EACH OTHER / ONE ANOTHER (reciprocal). If the sentence means "A did X to themselves and B did X to themselves" = REFLEXIVE (themselves/himself/herself). "They helped each other" = A helped B, and B helped A (reciprocal). "They helped themselves" = A helped themselves, and B helped themselves (reflexive). Number rule: TWO = each other (traditional). THREE OR MORE = one another (traditional). MODERN: interchangeable in many contexts. When in doubt in formal writing, apply the traditional rule.
Bryan López
Founder of SpeakUP Academy