Case Agreement for the Reciprocal Pron

The phrase ek-dusre is actually a compound. ek means "one" and dusre is the oblique form of "second/other". Because it almost always appears with a postposition (like ko, se, ke liye, ki), the second part is permanently stuck in its oblique form: dusre. You rarely see the nominative ek-dusra unless you're listing things (like "one is red, the other is blue"), which isn't a reciprocal usage. The critical rule is that ek-dusre takes the case marker demanded by the verb, just like any other noun.

1. 1Let's break down the mechanics so you never trip up:
2. 2Identify the Subject: It must be plural (Hum, Tum, Ve, Aap, or plural nouns like "The neighbors").
3. 3Select the Verb: Determine what postposition the verb usually demands (e.g., baat karna takes se, madad karna takes genitive ki, dekhna takes ko).
4. 4Apply the Compound: Use ek (invariant) + dusre (oblique).
5. 5Attach the Postposition: Glue the required postposition to dusre.
6. 6ek-dusre + ko = ek-dusre ko
7. 7ek-dusre + se = ek-dusre se
8. 8ek-dusre + ka/ke/ki = ek-dusre ka/ke/ki (Agrees with the *object*, not the subject!)

Use this whenever an action is a two-way street. If you are arguing, kissing, fighting, or exchanging gifts, this is your guy. It clarifies that A does it to B, *and* B does it to A. It's perfect for scenarios like resolving conflicts ("Let's listen to each other"), office dynamics ("Colleagues support each other"), or romantic confusion ("Do they like each other?").

Don't use it if the action is reflexive (apne aap). If you look in the mirror, you see *yourself* (apne aap ko), not ek-dusre ko (unless you're hallucinating another you). Also, avoid it if the action is one-sided. If I shout at you, and you sit there silently, we are not shouting at ek-dusre. We are just having a bad day.

• The "Nominative" Trap: Saying hum ek-dusra jante hain. No! It must be ek-dusre ko because janna (to know) takes an object. It's like wearing shoes on your hands—technically possible, but looks weird.
• The "Apna" Confusion: Using apna instead of ek-dusre. Hum apna kaam karte hain means "We do our (own) work," not "We do each other's work."
• Gender Bending: Trying to change dusre to dusri for females. The compound ek-dusre is fixed. Only the possessive particle (ki/ka) changes. Ladikyan ek-dusre *ki* madad karti hain (Girls help each other), NOT ek-dusri ki.

Compare ek-dusre with aapas mein. Aapas mein means "amongst ourselves/themselves" or "mutually." It's vaguer.

• Hum aapas mein baat karte hain (We talk amongst ourselves - general atmosphere).
• Hum ek-dusre se baat karte hain (We talk to each other - direct interaction).

Sometimes they are interchangeable, but ek-dusre stresses the individual one-on-one link within the group.