Henri Poincaré Quote

That being so what ought one to think of this question: Is the Euclidean Geometry true? The question is nonsense. One might as well ask whether the metric system is true and the old measures false; whether Cartesian co-ordinates are true and polar co-ordinates false.

Non-Euclidean Geometry, Nature, Volume 45, Number 1165, February 25, 1892 (p. 407)