The Stoics held two seemingly contradictory beliefs: that the universe is fully determined by fate (the causal network of Zeus), and that our beliefs, desires, and actions are “up to us.” Tad Brennan, a leading Stoic scholar, argues that resolving this tension requires abandoning the popular idea that our minds enjoy special causal exemption from determinism, and instead understanding “up to us” in a compatibilist sense—our actions are determined by our character, and that is sufficient for moral responsibility.
Fate: The Stoic Deterministic Universe
Fate as a causal network rooted in Zeus: The Stoics conceived of fate as a network of causes extending through all time and space, rooted in Zeus—the active, divine principle pervading all matter. Every event is caused by prior events, and this entire causal structure is orchestrated by Zeus.
Zeus is not simply “natural laws”: A key interpretive debate concerns whether Zeus operates like Newtonian natural laws (general, simple, predictable principles) or through something more like arbitrary individual fiats. Brennan argues the evidence does not require the natural-law reading. Zeus may determine each event individually without generalizable laws, much like entries in a prewritten book with no necessary connection between them.
This has ethical consequences: If Zeus works by arbitrary fiat rather than general laws, then Stoic ethics cannot be reduced to a set of universal rational precepts. Being virtuous would mean accurately following what Zeus wants in each particular situation—more like Abraham being commanded to sacrifice his son than like following the Ten Commandments.
Fate is providential: The Stoics also held that fate is benevolent—it is the best of all possible worlds, or at least directed toward the best. They justified this partly through theological arguments for the existence of a wise, virtuous, beneficent God, paralleling arguments later seen in Aquinas.
How the Stoics justified determinism: They offered three rational (not faith-based) arguments:
Bivalence: Every proposition, including future contingents (“it will rain in Ithaca next Thursday”), is already true or false. This entails determinism.
Causation: Every event has a cause; uncaused events are absurd (only Epicureans, with their atomic swerve, would accept them).
Divinity: A wise, beneficent God would providentially order the world.
Zeus and Logos are identical, but Logos need not be generalizable: While Zeus is the same as Logos (reason/nature), Brennan argues this does not mean Logos must take the form of general laws. The Stoic definition of a law is simply a proposition in imperative form (“thou shalt”), with no requirement of generality or regularity.
Secularizing Stoicism is hopeless: Brennan argues that removing the theological foundation from Stoic ethics distorts it beyond recognition. The Stoic account of human happiness—that it consists solely in the perfection of our rational soul, indifferent to bodily health or suffering—depends on the view that humans are literally fragments of Zeus (pneuma, the divine fiery breath). A secular version would need to ground the same radical anthropology (humans as purely rational, bodies as irrelevant to flourishing) without the theology, which is at best extremely difficult.
Control: What Is “Up to Us”
The popular Stoic pitch: The Stoics famously distinguish what is “up to us” (our thoughts, desires, beliefs, and the act of assent to impressions) from what is not (external events, the actions of others, our health). This is the basis of the practical advice to focus only on what you can control.
Assent as the core of psychology: All beliefs, desires, aversions, and emotions reduce to assent (or suspension of assent) to rational impressions. Seeing a cake produces the impression “this cake is desirable”; assenting to it creates the desire. The Stoics are extreme cognitivists—they believe emotions are constituted entirely by their propositional content plus assent, with no additional non-cognitive component.
The bait and switch: Brennan argues the Stoics are guilty of a fundamental bait and switch. Many passages (especially in Marcus Aurelius) suggest that assent is causally insulated from the deterministic nexus—a kind of inner citadel of freedom. But this cannot be the official Stoic view, because:
It contradicts their universal determinism (fate governs everything).
Their physics holds that the mind is made of the same material substance (pneuma) as everything else, not an immaterial soul exempt from physical causation.
Therefore, whether you assent to an impression is itself determined from all eternity.
What “up to us” really means: Assent is determined not only by external circumstances but also by your antecedent character. It is “up to you” in the sense that it is an accurate expression of who you are. You assent to eating the cake because you are the kind of person who does. This is a compatibilist account: responsibility comes from the action reflecting your character, not from having been able to do otherwise at that instant.
The practical asymmetry is about value, not causality: Brennan proposes that the real distinction between inner and outer is not causal (the inner is no more controllable than the outer) but evaluative. External failures (the door won’t open) do not affect your happiness; internal failures (assenting to false or harmful impressions) do. Happiness resides exclusively in the perfection of your faculty of assent.
Character can be slowly changed: While you cannot flip assent instantaneously, exposure to Stoic philosophy, good company, and reflection can gradually reshape your character, which will change your future assents. This is the slow path by which your inner life becomes “up to you.”
The inner and outer worlds are causally symmetric: Both are equally determined and equally subject to probabilistic influence. You can no more guarantee changing your own desires than you can guarantee opening a door. The Stoics were not inner-world isolationists—they advocated active engagement in politics, family life, and society.
Reconciling Fate and Control: Compatibilism and Its Limits
Moral responsibility compatibilism: The Stoics hold that you are blameworthy for actions that accurately reflect your character, even if you could not have done otherwise. When we call someone a glutton, we are judging their current character, not asking how they acquired it. Tracing the causal history of character (parents, culture) may assign further blame elsewhere, but does not exempt the agent.
Brennan’s dissatisfaction with compatibilism about deliberation: Brennan distinguishes between responsibility compatibilism (which he finds plausible) and deliberation compatibilism (which he finds much harder to accept). When we deliberate—should I walk, drive, or take the bus?—we naturally presuppose the future is open. Giving up that presupposition feels like losing something essential to the experience of choosing.
The Stoic account of deliberation as fact-finding: The Stoics reconceived deliberation not as creating an open future but as discovering what Zeus has already willed. You consider evidence (Do I need exercise? Is driving bad for the environment?) as clues to the already-fixed divine plan. Deliberation is like searching for your keys—the answer already exists; you just need to find it.
The lazy argument and its refutation: The lazy argument says: if I’m fated to recover, I’ll recover whether or not I call a doctor, so why bother? The Stoics respond that recovery and calling the doctor are co-fated—both are determined together. But Brennan notes this response arguably makes the problem worse, not better, since it reinforces that even your decision to call the doctor was determined from eternity.
Aristotle as a parallel: Brennan suggests Aristotle may have been a compatibilist about moral responsibility but an indeterminist about deliberation—a position he finds more honest than full Stoic compatibilism.
The Legacy of Stoic Compatibilism
Shrinking the self: The Stoics occupy a pivotal position in the Western tradition’s progressive narrowing of the self. They vacillate between two conceptions:
The “fat” self: I am my desires and beliefs; I am blamed for them because they are me.
The “thin” self: My desires are external to the real me, acting as constraints like chains or locked doors.
This vacillation influenced later philosophy: By sometimes treating desires as alien forces enslaving the self, the Stoics helped push the tradition toward requiring freedom from one’s own desires as the only genuine freedom. This reductive trajectory runs through Christian theology (the will as an isolated point) to Kant and modern philosophy.
Plato vs. the Stoics on the soul: Plato could more easily treat desires as external because he held that the soul is immaterial and exempt from physical causation. The Stoics, whose souls are material (pneuma), cannot coherently maintain this distinction—yet they are tempted by it.
The Stoics as a bridge: Brennan characterizes the Stoics as an oscillating bridge between the thicker Platonic-Aristotelian self and the radically thin modern conception of the will.
The Rationality of Humans vs. Animals and Children
Stoic cognitive extremism: The Stoics hold that all adult human mental life is structured by propositions and concepts. Even irrational urges (like compulsive cake-eating) involve conceptual content (chocolate, cake, goodness, eating). This is what makes humans “rational”—not that they are reasonable, but that their mental contents have propositional structure.
Animals lack rationality entirely: Unlike Plato (and Darwin), who saw continuity between animal and human psychology, the Stoics drew a sharp line. Animals do not have conceptual or propositional thought; their behavior is not structured by rational impressions and assent.
The problem of children: If rationality requires systematic conceptual content, children must lack it. Brennan reconstructs the Stoic view as follows:
Children accumulate proto-concepts (fuzziness, barking, dog-food) gradually, but these are not yet properly integrated into a conceptual system.
At a crystallization point (around age 14), all the proto-concepts suddenly gel into full concepts organized systematically. This is a Boolean (on/off) transition, not a scalar one.
Analogy to virtue and drowning: Just as two drowning people are equally drowned whether 5 feet or 5,000 feet below the surface, and just as virtue is an on/off state (you either have it or you don’t, with no degrees), so too rationality is a sudden threshold. A 13-year-old is no more rational than a toddler; at 14, the switch flips.
Brennan’s assessment: He acknowledges this story is speculative and the evidence thin, but argues it is the most plausible reconstruction of what the Stoics must have held, given their commitment to systematicity across multiple domains of their philosophy.
