# Why is an inflation rate of 2% optimal? [duplicate]

Learning from different sources I got the impression that the European Central Bank targets at a inflation rate of 2% (not sure along which time scale actually).

Can it be explained by general principles why a (long-term) inflation rate of 2% seems optimal?

Or does it depend on the current economic situation, and in some scenarios an inflation rate of 0%, 1%, or even 5% or deflation would be optimal (in the short or mid run)? But in the long run always 2%?