Studies concerning the history of Turkish language in the Ottoman period generally focus on works in literature and religion, and ignore works on logic, mathematics, astronomy, geography and philosophy of nature, whether written in Turkish or translated from Arabic, Persian or European languages. In conceiving the history of Turkish language, it is important to determine the motives and intentions of those who wrote in or translated into Turkish in various scientific disciplines. In those works, especially the prologues (dibace or mukaddime) and epilogues (hatime) give us valuable knowledge on the motives of authors or translators, as well as on their relation to Turkish. Here, first of all, Ottoman scholars' conception of 'language' and the place of Turkish in this conception are investigated. Then, the structure of the Turkish used by Ottoman scholar is examined. Finally, works in logic, mathematics, astronomy, geography and philosophy of nature of the period from the establishment of Ottoman empire to the groundbreaking reform, called Tanzimat, are examined with a view to the motives and purposes of their authors or translators in preferring Turkish as the medium.