'Act on impulse' or 'act on an impluse'
I picked up both expressions in dictionaries. Which one is more common?

Question

Answer

Both expressions work.  The choice may depend on the situation, and there is a slight difference in meaning.

"Act on impulse" is a more general expression of acting on impulses generally.  To "act on an impulse" means to take a specific action based on a specific impulse.

Answer

both, "Act on impulse" is more common.

Answer

Act on impulse is more common here because the language is often condensed to deliver the message faster

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