More often than in the case of any other sphere of culture, we face an apology of war while dealing with the history of philosophy. A lot of ancient and modern thinkers praised the phenomenon of war: among them are Heraclitus, Aristotle, Fichte, Hegel, Nietzsche, Vladimir Soloviev, Berdyaev, Sergey Bulgakov, etc. The author of the article attempts to reveal the causes of this phenomenon. In his opinion, some features similar to the mental prerequisites of wars are intrinsic to the very nature of philosophical discourse. Firstly, both philosophy and war share the cult of universal phenomena and the repulsion for everything private and individual. Secondly, both philosophical discourse and military practice employ a kind of “apophatic logic,” when unity is defined through the negation of independence and particularity. Thirdly, both philosophy and war are characterized by anti-utilitarianism, which clashes pragmatic interest against allegiance to the highest non-utilitarian values. These similarities between philosophy and war can be explained by their common function: both should defend the basic concepts of a particular community. Concepts lay the foundations for any religion and tradition, and are usually accepted without further consideration (while always being questioned by other communities). Therefore, war is an inevitable cultural phenomenon. Philosophy arises as a kind of compensation when a tradition is for some reason compromised by the members of the corresponding community. Philosophy exists either as a means of substantiation for a tradition or as a means for replacement. It strives for the revision of the basic set of concepts, but it is impossible to substantiate concepts by means of formal logic. And if a community stops accepting the basic meanings “automatically,” the only means of substantiation is violence (and war is its most radical form). Thus, for philosophy, war is a kind of substitute for argumentation. It is only natural that the majority of adherents to the idea of “eternal peace” ― from Henri de Saint-Simon to Vladimir I. Vernadsky - believed that such a peace is possible only if philosophical thinking will be substituted by scientific thinking (and this is, of course, a utopia).