Few figures were as qualified to mediate between European "Enlightenment" thought and a Muslim readership as Şemseddin Sami (Frashëri, 1850-1904)—a devout Muslim, Ottoman patriot, and prolific translator, novelist, and lexicographer. Trained in multiple intellectual traditions and fluent in more than half a dozen languages, Sami embodied the cosmopolitan intellectual currents of the late Ottoman Empire. Sami sought to bring Islam into dialogue with the rationalist and positivist philosophies he encountered in French thought, particularly among the Encyclopaedists. In his newspaper essays, pocketbooks, and his treatise Islamic Civilization, he praised Europe's "positive philosophy" (felsefe-i müsbete) as the triumph of reason over fanaticism, yet insisted that Islam was fully compatible with scientific inquiry and rational progress. His writings on medeniyet-i islâmîye ("Islamic civilization") expressed a historicizing vision that placed Islam within humanity's broader story of progress, while recognizing Western Europe as its contemporary center. For Sami, this compatibility implied that Islam was capable of renewal through reason. Sami's attempt to articulate a "rationalist Islam" was part of a broader late Ottoman effort to reconcile faith with reason, illuminating how intellectuals of his generation negotiated the shifting epistemic boundaries between religion and science in an age of global asymmetries. In this project, I examine his lexicon, monographs, and newspaper writings through the lens of conceptual history, focusing on how notions of "reason," "religion," and "spirituality" were redefined within his work. By tracing these shifts, I explore how, under emerging conditions of secularity, "Islam" itself became an object of rational inquiry and historical reconstruction.