Stoicism Is a Logical Philosophy

One hand grasps a fist, which is a symbol of katalepsis, of a graspable impression

Epistle 7. Posted on 2019-03-10. Edited on 2019-04-23.

Modern scholars misinterpret Stoicism as a moral philosophy, as predominantly about its ethics, virtue, or passions. This article challenges that scholarship, proposing instead that Stoicism is a logical philosophy.

Describing Stoicism as predominantly a moral philosophy is the same thing as describing the automobile as predominantly a gasoline-burning device. Although it is true that all automobiles (with the exception of electric automobiles) burn gasoline, and that all of those burn gasoline continuously while in operation (with the exception of hybrids), burning gasoline is not what an automobile is about. An automobile is about transportation.

Likewise, Stoicism is about logic. The tripartite division of the philosophy into logic, physics, and ethics is a division such that the student learns Stoic logic, then doctrines about physics that derived from Stoic logic, and then doctrines about ethics that derived from, you guessed it, Stoic logic.

In fact, Stoic logic, itself, reduces to a first principle.

The First Principle of Stoic Logic

The first principle of Stoic logic is the rejection of any conflict experienced from applying simultaneously two contradictory predicates to the same subject. The conflict experienced relates to the proposed contradiction: both p and not p.

Of these two contradictory propositions, one is true, the other false. The true proposition, provided it is caused by a body from a sensory impression (rather than a non-sensory impression) is also a proposition that is according to nature. The contradictory proposition is contrary to nature. The will (prohairesis) should be in accord with nature, and so if p represents nature, p should be wished; suffering is due to the will being contrary to nature, not p rather than p. By referring to two previous articles — Contradiction, and To Live Consistently — you can see the development from the motto of Zeno of Citium (c.334 BCE – c.262 BCE) to its next version, to live according to nature.

But more importantly, the rejection of any such conflict is the first principle of Stoic logic. The connectives are defined according to conflict, the five undemonstrated arguments are resolutions of conflict (and one reason why multiple propositions are required), and even Stoic modality is defined with conflict, but that is another story. In short, the system of Stoic logic is beautiful to me because it is defined with the rejection of contradiction, unlike modern mathematical logic which is a hodge-podge of ad hoc definitions and axioms, of arbitrary choices for connectives and other operators, and it is mathematical because it is defined with the likes of Boolean algebra, not the law of noncontradiction. Stoic logic is uniform, consistent, and based entirely on reason. Mathematical logic is a mess.

Modal Logic

Stoic modal logic differs sharply from modern modal logic. Stoic modal logic did not use operators, but evaluated the different modes of the truth of a proposition in relation to conflict, and in succession. Given the proposition Dion is a married bachelor, its semantic evaluation quickly results in a conflict between attempting to apply both married and unmarried to Dion, since a bachelor is defined as an unmarried male. Given the conflict, and that the first principle is that conflict is impossible in nature, this proposition is conceptually impossible (impossible given the definitions of its concepts).

But evaluate instead a proposition that is not in self-conflict, such as Dion is walking. Since there is no conflict, it is conceptually possible, on its own. But if another proposition contradicts it — such as Dion is lying down — the result may be that the external information in the other proposition forces you to evaluate the first proposition now as impossible.

But, the real interest is in the next modal dichotomy: between necessity and non-necessity. For that distinction, you will require the almighty Stoic conditional, which regards a connection, a connectedness really, between two events: an antecedent and consequent. And my favorite application is the graspable impression.

Graspable Impression

A graspable impression is a sensory impression in which the essential terms in the definition of the causing body are evident. If Dion sees a human, and if a human is defined as a rational animal, then for Dion to regard it as a graspable impression it must be evident that it is an animal, and that it is rational. If the human speaks understandably, that should satisfy both requirements, for example. Of course, many such impressions require testing that very definition.

This is, to me, the perfect epistemology. Your concepts are continuously revised throughout your life based on your experiences, and the criterion of the graspable impression is used to distinguish something that is necessary in nature given your concepts and associated definitions, from that which is non-necessary. It distinguishes knowledge from opinion. It does not guarantee absolute truth, the truth of what is in itself rather than the appearance of it, affected by perception, but nothing allows us to get at such absolute truth. The criterion of the graspable impression allows us to get as close to the truth about nature as we can, at the moment, and it is self-correcting over time, like science.


I cannot argue that every part of physics is derived solely from Stoic logic, but the vast majority is. The Stoics took the four elements on faith rather than deriving them, though perhaps there are books no longer extant that supported those elements.

The Stoics were, however, logical necessitarians, and this was due to Stoic logic. It is easiest to consider with the Stoic conditional. Consider a conditional such as If Both Socrates is mortal and Socrates drinks the hemlock, Socrates dies from it. Now, we all know that Socrates was mortal and that he did drink the hemlock. But due to the conditional, it is not just that Socrates died, but that it was conceptually necessary that he died from it. Stoicism, as I interpret it, argues that every effect has a causal explanation, and so every event is conceptually necessary. It is conceptually impossible for an event not to have occurred as it did. Put otherwise, every event can be explained in a conditional, is therefore necessary, and is grounded in other events. Fate, as the strings of necessity, is evidenced from the Stoic conditional. Some scholars have misunderstood Stoic modality and claimed that Chrysippus of Soli (c.279 BCE – c.206 BCE) was trying to escape from necessitarianism, or determinism.

Stoic causality is, after all, an explanation of the use of the Stoic conditional. And this concept of logical causality is superior to our modern causality, which requires a cause to precede its effect in time, or which allows a cause and effect to be interchangeable. If Dion sees the skid mark of a tire, he can conclude that a vehicle skidded there, and the future skid mark is a cause to the vehicle of having skidded there in the past, from his future perspective.

Stoic conceptions on time are also derived from Stoic logic. How thick is the surface of any body? Infinitely thin. Since any body must extend both in space and time to exist, no body has a surface; perhaps a surface subsists (in your mind), but it does not exist. How short is the present moment? Infinitely short. Therefore, there is no present moment. How Einstein would have enjoyed that.


Perhaps the beginning of Stoicism was when Zeno of Citium was studying Megaric logic, and realized that assenting to a proposition that contradicts nature — that is, to live inconsistently — is the source not only of being mistaken, but being unreasonable. Marcus Aurelius (121 – 180) describes it as insanity (Meditations, 11.38). Assenting to a contradiction is insanity. I suggest that Zeno of Citium dashed off for Athens to announce his new philosophy when he realized that the happy life is to live consistently, while noting that everyone lives inconsistently. O if Buddha could have founded such a solid footing.

Stoic ethics is also the domain of the original — and perhaps the only coherent — deontic logic. Stoic modal logic is its basis. Why are there three categories to things, such as virtues, indifferents, and vices? Because one is conceptually necessary, another contingent, and the other impossible with respect to an end. There is a little more to it than that, but that’s the rough idea.

It is also beautiful, to me, that the ethical philosophy of the Stoics emerged from a logical philosophy. I do not mean to imply that Zeno of Citium was neutral to the concept of ethics, and simply followed through with logic. But I am suggesting that he saw the connection between logic and ethics. It is also bedazzling that the moderns, from Frege and Bertrand Russell on, in the main, have missed this in its entirety, not strictly with Stoic logic, but with logic, period.


This has been a casual presentation of my interpretation of Stoicism. I realize this article probably raises more questions than it answers, and I apologize for that. I have been working on a book for a few years now that is more formal and technical, exploring Stoicism from the perspective that it is a logical philosophy. Since this book will not be ready anytime soon, I have posted this article to claim my ideas publicly, and to encourage scholars to start pursuing this interpretation. Stoicism is, I must assure you, a logical philosophy.

Vale (pronounced WAH-lay is Latin for Farewell),

Ron Hall

Ron Hall

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