2 8 6 D O C U M E N T 2 9 2 O C T O B E R 1 9 2 8 292. To Hans Reichenbach Berlin W, 19 October 1928 Dear Mr Reichenbach, I think the logical presentation that you give of my theory is indeed possible, but it’s not the simplest one.[1] It seems to me that the following is the best logical clas- sification: One only considers theories for which the local comparison of vector magnitudes makes sense. (Nullmetric, the are only determined up to a constant factor.) For manifolds of this kind the following possibilities of increasing specialization regarding the distant comparison of vectors are possible:[2] 1. Neither the distant comparison of the magnitude nor that of the direction makes sense (Weyl) 2. Distant comparison of the magnitude, but not of the direction, makes sense (Riemann.) 3. Distant comparison of the direction, but not of the magnitude, makes sense (not yet investigated.) 4. Distant comparison of both the magnitude and of the direction makes sense. (Einstein.) Of course, one can also start with an affine connection and specialize either by introducing a metric or by introducing integrability conditions, as you have done. But this is less simple, less natural.— The naturalness of the field structure that I envisaged seems indisputable to me. I will only know in a few months whether this construction contains deeper traits of reality, since the problems needed to be solved to make this decision are not at all easy.— Best regards, your A. Einstein P.S. I would be delighted if you and your wife could come to tea on the 5th. Schrödinger is supposed to come as well.[3] g 