Meine Finger werden warm, sobald sie mit ihren Händen arbeitet.

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Breakdown of Meine Finger werden warm, sobald sie mit ihren Händen arbeitet.

• arbeiten: to work
• warm: warm
• sie: she

Questions & Answers about Meine Finger werden warm, sobald sie mit ihren Händen arbeitet.

Why does the sentence use werden warm instead of sind warm?

Werden with an adjective (warm) expresses a change of state: “werden warm” = “to become/get warm.”
If you said “Meine Finger sind warm”, it would just describe a state: My fingers are warm (already).
“Meine Finger werden warm” focuses on the process: they are starting to get warm.

What exactly does werden mean here? Is it the future tense?

Here werden is not a future-tense auxiliary; it is a full verb meaning “to become” / “to get.”
So “werden warm” literally means “become warm.”
The German future tense would be “Meine Finger werden warm werden” (they will become warm), but that would sound very unusual here.
In everyday German, present tense often covers future meaning, so context decides whether werden is “will” or “become.” Here it clearly means “become.”

Could the sentence also be “Meine Finger sind warm, sobald sie mit ihren Händen arbeitet”?