4 4 8 D O C U M E N T 4 5 4 J A N U A R Y 1 9 2 7 something new begins in this respect, because for any arbitrary small densities there already is an abnormal filling of the lower quantum states, compared to the Boltzmann distribution, and with rising density it becomes ever worse but in this regard there isn’t any singular density at all at which anything new starts AND THAT’S WHY I deny that any kind of analogy to a two-phased system exists in which at a definite density something really especially new happens. Oh, you in- corrigible fellow!!!!!!!!! This shouldn’t be taken as some kind of compliment! I permit myself to send you the enclosed manuscript of a letter that I sent to Berliner for the Naturwissenschaften a few days ago. I attempt to demonstrate: from the impenetrability of material particles, the Schrödinger equation NECESSARILY yields the Pauli exclusion principle. 454. To Hedwig Born [Berlin,] 15 January 1927 Dear Mrs. Born, I gave your manuscript a few days ago to Jessner, who already promised to ex- amine it. You should not take my little joke too seriously, and not according to the either-or principle. It is neither meant so very seriously, nor does it make a claim to the unambiguousness of the intended assertion: one grins and goes back to the day’s agenda. As with jokes, so it also goes a bit for pictures and plays. I be- lieve they ought not have the flavor of a logical scheme, but rather of a delicious slice of life, sparkling in different color shades depending on the perspective of the observer. If one wishes to get away from this blurriness, one must just do mathe- matics. And even it reaches this goal only due to the fact that it becomes totally free of substance under the scalpel of clarity. Lively content and clarity are opposites, one abandons the field to the other. We are now tragically experiencing precisely that in physics.— Incidentally, you need not defend your work to me. For I have great respect for it and find pleasure in it. One seldom finds a wealth of ideas combined with grace- fulness as with you. Good luck in your efforts, and warm wishes to you and to yours, your A. Einstein Many thanks for the delightful combination pictures.