This is not true of all Jewish medieval scientists—only those living in the Arab world (the Middle East, North Africa, and Spain-Portugal), where of course Arabic was the lingua franca.
Arabic was also the language in which the ancient writings of ancient Greece and Rome—particularly those related to science, medicine, and non-religious philosophy—were preserved during the Middle Ages while Europe was mired in endless internecine warfare, and the only literate people (mostly Christian monks and clerics) were absorbed exclusively in Christian theology. Hebrew was used by Arab Jews mainly for prayer, study of the Hebrew Bible and Talmud, and communication with other (mainly non-Arab) Jews.
When Europe finally began to awaken from its intellectual torpor, it rediscovered the ancient Greek and Roman works mainly through their Arabic translations. These, along with the original works of centuries of Arab scientists and philosophers—such as Al-Khwarizmi (a.k.a. Algoritmi), Ibn Sina (Avicenna), Ibn Khaldun, and many others—eventually paved the way for Europe’s Renaissance. (For more information see, for example, Maimonides, and , and .)
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