Stoicism as a Warrior Philosophy: Insights on the Morality of Military Service

by William C. Spears

Can ancient philosophers really provide useful insights for the modern warfighter?
How might they reconcile cosmopolitan principles with patriotic duty?
Would a truly enlightened individual participate in the horrors of war?

Stoicism as a Warrior Philosophy grapples with these questions and more. Authored by a serving military professional, it breaks down the most advanced concepts of Stoicism into plain language without oversimplifying. Exhaustively researched, steeped in original sources, and informed by examples from the cutting edge of modern conflict, it builds upon ancient thinking to develop innovative theories of patriotic duty and ethical warfighting.

While Stoicism has seen an explosion in popular interest, and is widely embraced in military culture, no serious philosophical work has yet explored its full implications within the military profession. This book answers that call. Endorsed by senior military officials and academic philosophers, Stoicism as a Warrior Philosophy provides compelling and original contributions to both military ethics and the literature of modern Stoicism.

Genres: Military Fiction, Philosophy

288 pages, Paperback

Published November 13, 2025

About the author

Commander William C. Spears is a submarine warfare officer in the U.S. Navy, author, and independent scholar who writes on leadership, ethics, and military affairs.

A native of Pineville, Louisiana, William enlisted in the Navy’s nuclear propulsion program before earning an appointment to the U.S. Naval Academy, where he graduated in 2008 with a degree in Mechanical Engineering. He also holds advanced degrees from the Naval Postgraduate School, the Air Command and Staff College, and the Eisenhower School. He has served aboard multiple nuclear-powered submarines, including as Weapons Officer on a fast-attack submarine and Executive Officer of a Trident submarine, and has held staff and evaluation roles ashore. He is married with three children.

Reviews

[Nick · Rating 5 out of 5]

Stoicism as a Warrior Philosophy was not quite the book I expected, and that turned out to be a pleasant surprise. Rather than offering a shallow collection of Stoic quotations, aphorisms, and modernized lessons in resilience, William C. Spears provides a thoughtful treatment of Stoicism as both a historical philosophy and a practical system for living. He examines where Stoic thought remains useful today, particularly for those engaged in military service, while also being refreshingly candid about those aspects of the philosophy that do not model reality especially well. I appreciated that honesty. Spears does not simply sell Stoicism to the reader; he wrestles with it.

My primary takeaway was not that Stoicism provides a complete philosophy I would want to adopt, but that it contains a number of practical disciplines and ethical insights worth considering. I am always interested in how the different aspects of life - our understanding of the world, ethics, duties, commitments, vocation, and daily conduct - can be brought into coherent alignment. Spears repeatedly touches that larger question even while maintaining his focus on the warrior. I found the book valuable both historically and practically, and my own approach would be to retain those Stoic principles that align well with my Christian ethics while leaving behind those portions of the system that do not.

Full Review

Spears begins from the warrior, but his subject quickly becomes broader than military service alone. Stoicism is presented not merely as a collection of techniques for enduring hardship but as an attempt to provide an integrated model for living. That distinction matters. Modern popular treatments of Stoicism can sometimes reduce the philosophy to self-discipline, emotional control, and memorable quotations from Marcus Aurelius or Epictetus. Spears takes the philosophy much more seriously. He provides enough historical grounding to explain how the ancient Stoics understood virtue, duty, reason, fate, community, and the proper conduct of life, and then subjects those ideas to the realities of modern military service and modern ethical questions. The result is a considerably more substantial examination than I anticipated.

The military application is nevertheless one of the book's strengths. Stoicism has an obvious attraction for the warrior because of its emphasis upon courage, endurance, duty, self-command, acceptance of circumstances outside one's control, and the requirement to act rationally rather than impulsively. These qualities translate readily into the demands of military service. But Spears does not stop with the easy parallels. The more difficult questions concern when duties compete, where moral authority resides, how loyalty should be understood, and whether the ancient Stoic framework can adequately address the realities encountered by the modern warrior. At several points Spears appears to thread a fairly narrow ethical needle in order to preserve the fundamental strengths of Stoicism while acknowledging where the original philosophical system requires qualification. I viewed that as a strength rather than a weakness because he seems more interested in determining what remains defensible than in protecting Stoicism from criticism.

The portion I found most unexpectedly interesting concerned the tension between community and cosmopolitanism. I was surprised that this ethical problem was being debated so vigorously more than two thousand years ago. We tend to underestimate our ancient forefathers, sometimes assuming that because they lacked our technology they also lacked our intellectual sophistication. The Stoics were already wrestling with questions that remain very much alive today: What do we owe our family, community, political society, and nation, and what do we owe humanity more broadly? Particular loyalties matter because people actually live within families, communities, institutions, and nations where concrete obligations arise. Yet the Stoic cosmopolitan impulse insists that membership in a particular community cannot entirely define the limits of moral concern. Spears' discussion of how these competing obligations are negotiated provides an unexpectedly useful lens through which to consider today's debates surrounding nationalism, globalism, and political identity. The vocabulary has changed considerably; the underlying struggle has not.

The warrior makes that tension especially clear. Military service is inherently particular: one serves a specific nation, accepts a defined chain of command, defends particular people and institutions, and may be required to fight those serving another political community. Yet those obligations do not eliminate broader moral duties toward civilians, prisoners, the wounded, or even enemy combatants. Much of what we regard as honorable conduct in war depends upon maintaining both ideas simultaneously. In that respect, Stoicism provides an interesting framework for thinking about how particular duty and universal moral obligation coexist. I ultimately find Christianity to provide a more complete foundation for resolving those questions, particularly through its understanding of vocation, moral authority, human nature, and the worth of the individual. Even so, Stoicism offers useful disciplines for governing oneself and thinking carefully about duty, courage, restraint, adversity, and responsibility.

That is ultimately how I came away from Stoicism as a Warrior Philosophy. Spears gave me considerably more than a study of military resilience or an introduction to ancient Stoic sayings. He presented a serious philosophical tradition, explored how it attempted to construct an integrated way of life, identified where that system encounters difficulties, and demonstrated where portions of it remain useful today. I would not adopt Stoicism holistically, but I found considerable value in examining its architecture and taking from it those practices and insights that reinforce a sounder ethical foundation. For readers interested in military ethics, Stoicism, the history of ideas, or simply the enduring problem of how to bring belief, duty, conduct, and community into alignment, Spears has produced a thoughtful and worthwhile book.

[Phil Yanov · Rating 5 out of 5]

If you have been hanging around Stoic circles for a while, you know there is a big difference between scrolling through motivational quotes on Instagram and actually doing the work. William C. Spears’ Stoicism as a Warrior Philosophy is strictly for those interested in the latter—especially if your "work" involves high-stakes environments like the military or first response.

I picked this up for a group I facilitate, looking for something that went deeper than the usual introductions, and I wasn't disappointed. Spears doesn't just skim the surface; he offers a rigorous, structured framework for the "warrior-philosopher."

Here is what stood out to me, and why I think this belongs on your shelf:

1. It treats Stoicism as a complete system.
Spears organizes the book around six pillars: Mission, Excellence, Discipline, Duty, Country, and Warrior. He doesn't shy away from the "weird" stuff, either. He dives right into Stoic metaphysics (God, Nature, Fate) in the first chapter. He argues—rightly, in my opinion—that you can't really understand the ethics if you don't understand the worldview that built them.

2. The "Stoic Knife."
This was my favorite concept in the book. We often talk about the "Dichotomy of Control," but Spears reframes it as a "knife" that allows you to surgically cut away the past, the future, and all external opinions, leaving you with only your immediate capacity for choice (prohairesis). It is a much more active, aggressive visualization for keeping your head in the game.

3. A Sane Approach to Duty and Patriotism.
The chapters on "Duty" and "Country" tackle the hard questions about how to balance loyalty to your unit or nation with your duty to humanity as a whole. Spears uses the concept of oikeiōsis (expanding your circle of care) to show that being a patriot and being a cosmopolitan aren't mutually exclusive—they are parts of the same ladder.

4. Confronting Moral Injury.
The final chapter is heavy but necessary. It argues that guilt over past justified actions is logically inconsistent for a Stoic. It frames the warrior not as a mindless cog, but as an autonomous moral agent who must retain the judgment to obey, or disobey, based on natural law. For anyone dealing with the weight of service, this perspective offers a lot of resilience.

A Gentle Warning for Readers:
While the book is fantastic, keep in mind that it is philosophical, not clinical. The Stoic ideal of apatheia (freedom from passion) and the rejection of remorse are high bars to clear. It describes the ideal Sage, but we are all just progressors on that journey, trying to get a little better every day.

The Verdict:
If you are tired of "fluff" philosophy and want a manual that respects the brutality of the real world while aiming for the highest moral good, read this book. It is an excellent resource for cultivating that virtues we all need to face life’s battles.

Highly Recommended.

[Carlos Negroni · Rating 5 out of 5]

Incredible book. It’s well researched and well written. A fresh look at a centuries of academic material presented in a relatable, but also thought provoking fashion. A must have in every leaders book shelf. I wouldn’t be surprised if this ends up on the CNO or JCS book list one day.

[Franklin Annis · Rating 5 out of 5]

Typical works on Stoic philosophy focus their attention on Stoic ethics. This might be argued to be the enduring wisdom of the ancient philosophy that still holds value in our contemporary era. However, William Spears examines ancient Stoicism in its entirety, including discussions on Stoic logic and physics.

As explained by Spears, Stoic logic serves as the foundation of their philosophy. It places emphasis on the importance of reason and rational thinking. Stoic philosophy held that discerning and reasoned thought enables a more profound understanding of the world, thereby facilitating sound decision-making. The Stoics formulated an intricate system of logic encompassing theories of perception, language, and knowledge. This rational method was vital for discerning between valid and invalid beliefs, essential for attaining wisdom.

Within philosophy, physics denotes the examination of the natural world and the universe. The Stoic perspective held that the universe exists as a rational and interconnected whole, subject to divine reason, or logos. They posited that all events occur in accordance with natural laws, and comprehension of these laws facilitates personal alignment with the natural order. This viewpoint cultivates acceptance and serenity, acknowledging events are uncontrollable and should be met with composure.

Ethics constitutes the applied dimension of Stoic philosophy. It emphasizes the importance of virtuous living, guided by reason and nature. Stoic philosophers recognized four principal virtues: wisdom, courage, justice, and temperance. Through the cultivation of virtue, individuals may attain eudaimonia (happiness), leading to a flourishing existence. Stoic ethics posit that genuine happiness originates internally and remains independent of external factors. This internal strength allows people to safeguard their moral compass and inner harmony, no matter the trials of life.

While Spears’ comprehensive examination of ancient Stoicism provides significant strength to this book as an academic work, it may be a weakness in exploring Stoic ideas through time. Spears wrote a book specific to ancient Stoicism, a philosophical school locked within a specific timeframe. This unfortunately hampers some of his discussions later in his work trying to relate Stoicism to the needs of modern warriors. While he relates ancient Stoicism to the warrior’s responsibilities to follow the laws of war, Spears misses the opportunity to discuss how the laws of war grew out of the NeoStoic tradition. NeoStoicism was a philosophical movement, started in the late 16th century by Justus Lipsius, who reconciled ancient Stoic ethics with Christian theology. The NeoStoic Hugo Grotius, “the father of international law,” wrote the “first general comprehensive modern work grounded on reason and natural law” with his De jure belli ac pacis (On the Law of War and Peace). Spears should not be faulted here because there is only so much one can put into a single book. The quality of Spears’ research on ancient Stoicism is more than sufficient to make his work a valuable resource for anyone interested in military Stoicism.

While Spears advocates the self-study of Stoic philosophy, he does not promote the military teaching this philosophy as a standardized course. In my private conversations with Stoic educators, there has been a genuine fear expressed that instructors who are not invested in this philosophy would do a poor job of explaining it to new recruits. This could cause service members to reject the philosophy out of the failures to motivate learners common with military instruction. Spears also is hesitant to deal with the theological references in ancient Stoic physics. Modern Stoicism (a philosophical school developed in the last 60 years) does not take as full of a look at the philosophy as Spears, as previously discussed. Modern Stoic materials typically address Stoic ethics which could resolve some of these issues. There are surely forms of modern Stoicism that can support the range of religious beliefs from atheism to polytheism. The Stoic-based Before Operational Stress (BOS) program developed by Dr. Megan McElheran of Wayfound Mental Health Group might be a powerful example for the military in how Stoic instruction might be best integrated into a psychological resiliency program.

If placed on the continuum of Stoic materials for a new student of this philosophy, Spears’ Stoicism as a Warrior Philosophy it would certainly be towards the middle, between popular light reads and heavy academic investigations. While this could be used as an introduction to Stoicism, the depth of this work would probably be better suited to someone that had already read a contemporary intro to Stoicism like Donald Robertson’s How to Think Like a Roman Emperor and at least a few of the primary sources, like Marcus Aurelius’ Meditations, Epictetus’ Enchiridion, and Seneca’s Letters from a Stoic. Nonetheless, Spears’ work is worth to reading before exploring the effects of Stoicism on the creation of the American Republic, as is found in works such as Goodman and Perkins’ Rome’s Last Citizen. For further information on the influence of Stoic philosophy on early American military education, Controversial History & Educational Theories of Captain Alden Partridge (Marching with Spartans: The Life and Works of Alden Partridge VOL I) provides further materials on the evolution of Stoic thought that wasn’t included in Spears’ work.

To conclude, William Spears’ Stoicism as a Warrior Philosophy constitutes a valuable resource for any service member or scholar seeking a deeper understanding of ancient Stoic philosophy. This text is infinitely superior to Nancy Sherman’s Stoic Warriors, in discussing ancient Stoicism and the modern service member. It is obvious Spears invested significant time and attention to detail in his research, attempting to reconcile contemporary military service and this incredibly powerful philosophy. The hope is that Spears’ example will inspire other service members to dare to be military philosophers to further advance the profession of arms.

This review was first published in the Small Wars Journal

[Ben Powers · Rating 5 out of 5]

"Stoicism as a Warrior Philosophy" is a new contribution to the Stoic literature that explains the philosophy’s major tenets and offers practical advice for how military professionals can apply them to address the challenges of the modern operational environment. William C. Spears, a serving naval officer, has a hard-won understanding of the moral conundrums that confront service members, and he effectively applies the words of Stoicism’s ancient practitioners to show how to make morally grounded choices. Spears’ efforts go deeper than much of the popular culture Stoicism that is currently popular on social media. He invites readers to examine the responsibilities of leadership through the lenses of wisdom, justice, courage, and temperance.

Spears claims that Stoicism is a complete ethical system that military members can use as a compass to navigate ambiguous situations. He delves into notions of obedience, unlawful orders, and physical & moral courage. He makes ancient ideas accessible to a contemporary audience and speaks with the authority of a professional officer. Spears addresses the idea that an officer must maintain their own sense of morality despite being part of an established chain of command and be prepared to use violence without becoming corrupted by it. Spears highlights that each of us is responsible for being just, despite operating in an unjust world. He does not pull punches or obfuscate his points in philosophical language. Spears has obviously immersed himself in Stoic literature, and that preparation, combined with his CV, provides him with an air of authority that will resonate with a military readership.

Spears avoids a review of Stoic philosophy as it has evolved over the centuries, which may be seen as a limitation by more knowledgeable readers who understand Stoicism's evolution and its influence on modern theories of conflict and international law. He focuses on using the philosophy as an ethical framework for contemporary military personnel. In this, he succeeds remarkably well. Stoicism as a Warrior Philosophy belongs on the bookshelf next to Stockdale’s "Thoughts of a Philosophical Fighter Pilot".

[Chad Manske · Rating 4 out of 5]

William C. Spears’ “Stoicism as a Warrior Philosophy: Insights on the Morality of Military Service” is less a conventional philosophical treatise and more a field manual for the morally serious professional in arms. Spears, a Marine officer with academic grounding, bridges Epictetus and Fallujah with an ease that feels earned rather than forced. The book’s core strength lies in its refusal to romanticize either Stoicism or military service. Spears treats Stoicism not as a set of comforting aphorisms, but as a demanding discipline—one that requires clarity about control, responsibility, and the moral weight of violence. His reading of Stoic ethics is pragmatic: virtue is not abstract excellence, but the steady alignment of judgment and action under conditions of fear, uncertainty, and consequence. What makes the work particularly compelling is its implicit dialogue with just war theory. Spears does not discard traditional frameworks, but he shifts the center of gravity from institutional legitimacy to individual moral agency. The question is not merely whether a war is just, but whether the warrior acts justly within it. That distinction resonates in an era of decentralized operations and strategic ambiguity. Spears is at his best when discussing moral injury. He frames it not simply as trauma, but as a rupture between one’s actions and one’s moral expectations—a gap “Stoicism” is uniquely equipped to address. His argument that disciplined reflection, rather than emotional suppression, is the Stoic path will likely strike readers as both corrective and actionable. If the book has a limitation, it is that its brevity occasionally leaves deeper philosophical tensions underexplored. Readers looking for rigorous engagement with competing ethical systems may find the analysis somewhat selective. Even so, Spears delivers a sharp, relevant contribution to the ethics of military service—one that speaks directly to those who must make consequential decisions in imperfect conditions. It is a compact but serious meditation on how to live, and act, well in war.

[Ryan Driscoll · Rating 5 out of 5]

As someone who studies Stoicism seriously, and who served in combat operations as an infantryman, this is one of the best books on Stoicism I have read from modern writers. Spears spends considerable energy researching and laying out the original Stoic perspective and then uses them to articulate specific arguments related to the military. Attempting to stick to what the Stoics thought when making the arguments allows the reader to judge for themselves the compatibility, without having to discern how much of the author's personal opinions are injected without note. With the caveat that all modern writing should be scrutinized for coherence with the extant writings of the Stoics and their critics.

His interpretations of some of the Stoic positions, and the way he articulated them, helped me clarify my thinking on several positions. There were also several points of disagreement I have with his interpretation, but none of them can be said to be careless (and I could be wrong).

This book is written for non-experts but doesn't pull any punches on technicalities or academic citations. It isn't a self-help book; it is a detailed review of the compatibility of Stoicism with the role of warrior. Conveniently, in handling the complex question of how one can be a warrior in a cosmopolitan philosophy, William lays out a structure for analyzing conflicts in roles and responsibilities and how to discern appropriate action that extends far beyond the concept of military service.

I would recommend this to any philosophically minded soldier, anyone seriously interested in the applicability of Stoicism to life, or anyone who thinks that considering this topic is foolish and contradictory.