This paper analyzes Mustafa Kemal Ataturk’s much neglected book Conversation with “Officer and Commander” written in 1914 while serving as military attaché in Sofia. In it, Mustafa Kemal outlined his main ideas about leadership and war. In this paper, I focus on two critical concepts in his military thought: the “intellect” (dimag) and “conscience” (vicdan). Intellect helps direct an army in war and guides officers in taking initiative. Conscience calls forth the highest ideals of the profession, including patriotism and religious faith. A careful reading of the Ottoman original published in 1918 shows the passion behind these two concepts in Mustafa Kemal’s thought and character. Intellect and conscience help explain Mustafa Kemal’s earlier decision to translate two German manuals for small unit tactics (1909-1911). The second half of the paper shows how Mustafa Kemal applied intellect and conscience as Commander-in-Chief (Ba?komudan) in the critical Battle of Sakarya (23 August to 13 September 1921) during the Turkish War of Independence (1919-23). Here I critically dissect the order issued by Mustafa Kemal three days before the battle (20 August) for dissemination to all units and then address how he responded to the loss of Mangal Mountain in the second day of combat. This part of the paper is based on primary source material obtained at the General Staff Directorate of the Archives of the Military History and Strategic Studies in Ankara. The discussion of intellect here is linked to a statement by the Prussian military theorist Carl von Clausewitz (1780-1831) on the essence of military genius. The paper ends by suggesting that an understanding of intellect and conscience in Mustafa Kemal’s military career provides insight into the subsequent reforms under Ataturk’s statesmanship as President of the Republic of Turkey.