which is which

idiom

—used to say that one is unsure about the identity of each member of a group
One of the twins is named John and the other William, but I don't know which is which?

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Related Articles They are organized by section — skirt suits, white, leather, exotic materials — but correctly identifying which is which could stump even the most dedicated fashionphile. — Joelle Diderich, WWD, 3 Mar. 2025 Won-Young is able to discern which is which—and which of the lost souls that wander into his shop might just be trapped between the two worlds. — Ars Technica, 24 Dec. 2024

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which is to say
which is which
whichsoever
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“Which is which.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/which%20is%20which. Accessed 2 Apr. 2025.

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