In April 1953 Einstein replied to J. S. Switzer, a retired army officer studying for a history degree at Stanford, who had asked why modern science did not arise in China. The reply runs to two short paragraphs.

Einstein named two foundations. The first was the formal logical system devised by Greek philosophers and embodied in Euclidean geometry. The second was the discovery, during the Renaissance, that causal relationships could be established through systematic experiment. He then reversed the terms of the question: the absence of these steps elsewhere required no explanation, whereas the fact that they were taken at all was the surprising thing.

The letter reached a wide audience through Derek de Solla Price’s Science Since Babylon and is often cited in debates around the Needham question.