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in the us and japan. this is no coincidence. there is a robust rationale for aiming at 2 % or close to 2 % and, therefore, not tolerating persistent lower inflation. first, since the work of the boskin commission, which, i believe, is also valid for the euro area, we know that available measures tend to overestimate this rate. so it is legitimate to consider that, technically, an inflation rate of 1 % may, in reality, be zero. then, if the central bank aims at 1 %, any negative shock would plunge the economy into deflation. to absorb such a shock, some margin – in the order of an additional 1 % – is necessary. this simple reasoning provides a very strong basis for the current definition. the objective of price stability, therefore, must be symmetric. the reaction function of central banks should equally be perceived as symmetric. they should be equally vigilant about any deviation from this objective, in either direction, up or down. a central bank that remained passive with persistently low inflation would in effect encourage a downward drift in expectations. the case for symmetry is even stronger today as we are confronted with several sources of uncertainty, regarding : the economic situation ; the transmission mechanism of monetary policy ; and the underlying causes for low inflation. we should avoid adding a further uncertainty concerning the true priorities of central banks. for the same reason, it would be unwise to entertain the idea that the inflation objective should be revised, – upward or downward. the analytical argument for a higher target sounds attractive. for a given equilibrium real rate, a higher inflation objective would reduce the probability of hitting the zero lower bound in the future. this may be a case, however, where analytics do not provide a proper guide for policy. the truth is we do not know how inflation expectations would react to a change in objective. we are in a period where expectation dynamics are highly uncertain. empirical evidence collected over the last 15 years shows that, in the euro - area at least, a rate of inflation significantly over 2 % triggers very negative reactions from the general public. finally, the credibility of central banks in sticking to their objective could be jeopardized by the change of definition of price stability. and that would generate risk premia and additional volatility in financial markets. the challenge in achieving price stability implementing a symmetric mandate in current circumstances is not an easy task. i see three challenges in the current situation first, in finding the