He was probably right

The article begins by introducing Marcus Tullius Cicero, a Roman statesman, lawyer, and philosopher, who lived from 106 to 43 BCE. In 45 BCE, Cicero wrote Academica, a philosophical work explaining Academic Skepticism, a school of thought he adopted. This period was tumultuous for Cicero: his political ally Julius Caesar declared himself dictator for life, leading to Caesar's assassination in 44 BCE. Personally, Cicero had recently divorced his wife of 30 years and suffered the loss of his daughter Tullia in 45 BCE. Despite these crises, Cicero wrote extensively, influencing medieval Christian scholars, Renaissance thinkers, and the Founders of the American Republic. His Academica addresses the balance between doubt and certainty in belief, a topic explored through his own experiences and philosophical arguments.

Academic Skepticism traces its roots to the Platonic Academy, founded by Plato in Athens around 387 BCE. The school was later led by Philo of Larissa, who visited Rome in 87 BCE and inspired the young Cicero. Unlike Plato’s focus on abstract metaphysics, the New Academy emphasized practical inquiry, building on Socrates’ method of questioning. Key figures like Arcesilaus and Carneades, active in the 3rd and 2nd centuries BCE, argued that human knowledge is fallible due to the limitations of the senses and reason. They did not advocate for absolute skepticism but proposed that actions should be based on what is persuasive or plausible, a concept Carneades called pithanon in Greek. Cicero later translated this into Latin as probabile (plural probabilia), meaning claims that withstand scrutiny and are worthy of approval, even if not certain.

Probabilia refers to beliefs that are not certain but are well-supported by evidence and reasonable to act upon. Cicero described it as holding many things to be probabilia, which can be followed easily but affirmed rarely. Unlike modern statistical probability, probabilia means a claim that a reasonable person would approve of while remaining open to revision. Carneades further graded impressions into four levels: first, simply more likely than not; second, persuasive; third, undiverted (no conflicting beliefs); and fourth, thoroughly examined, akin to scientific investigation. For example, trivial matters might only require the first or second level, while medical or legal decisions demand the third or fourth. This grading system allowed for calibrated confidence in beliefs and actions.

The article contrasts Academic Skepticism with Pyrrhonism, another ancient skeptical school. Both schools doubted the possibility of certainty, but they differed in their approaches. Pyrrhonists, like Pyrrho of Elis (c. 360–270 BCE), aimed for ataraxia (tranquility) by suspending judgment on most issues and acting according to appearances or local customs. In contrast, Academics like Cicero assented to beliefs in a weakened sense, taking responsibility for their actions even if they might be wrong. Academics also ranked beliefs by how much scrutiny they had survived, allowing some to be more reliable than others. While Pyrrhonism sought peace of mind, Academic Skepticism pursued truth through fallible but actionable judgments, making it more suited for practical decision-making in a complex world.

The article outlines six practical habits derived from Cicero’s probabilia method for holding beliefs in a balanced way. First, express confidence levels explicitly, such as stating a belief is 7 out of 10, and explain what limits that confidence. Second, grade beliefs by how rigorously they have been tested, reserving confident action for higher-grade beliefs. Third, separate values (e.g., children should not go hungry) from empirical claims (e.g., a specific school-meals program reduces hunger), as conflating the two can lead to defending flawed policies. Fourth, state in advance what evidence would change your mind; if nothing would, it may not be a belief but an identity. Fifth, argue both sides of an issue thoroughly, as the Academy’s exercise of in utramque partem (on both sides) helps clarify one’s own stance. Finally, act despite uncertainty, treating being wrong as data rather than failure, as uncertainty is a permanent condition of human decision-making.

Cicero applied his skeptical method to real-life decisions, including his actions as Consul of Rome in 63 BCE. Facing the Catiline Conspiracy, a plot to overthrow the government led by Lucius Sergius Catilina, Cicero gathered evidence and acted on probabilia. He convinced the Senate to pass an emergency decree, senatus consultum ultimum, and debated the fate of captured conspirators. While his actions were later contested and led to his temporary exile, Cicero defended his decisions without claiming certainty. He also applied his method to superstition in De divinatione, examining Roman practices like augury and haruspicy (reading entrails) without dismissing them outright. Instead, he asked for evidence of their mechanisms and reliability, a practice later echoed by Carl Sagan’s principle that extraordinary claims require extraordinary evidence. His letters to Atticus before his death in 43 BCE further illustrate his reasoning under uncertainty, such as deciding whether to flee or return to Rome despite the risk of assassination by Mark Antony.