§5 Reasonable Beliefs and the Ethics of Belief

Being a Reasonable Person is not just about the mechanics of logic; it is a moral and intellectual commitment. This final section explores how we decide what constitutes a “reasonable” level of evidence and the ethical responsibility we have for the things we choose to believe.

5.1 The Standards of Rationality

Not all beliefs require the same amount of proof. The level of justification required is often determined by the stakes of the situation.

• The Preponderance of Evidence: In everyday life and civil law, we often accept a belief if it is “more likely than not” (51% certainty).

• Beyond a Reasonable Doubt: In criminal law or high-stakes science, we require the evidence to be so strong that no logical alternative seems plausible.

• The “Sagan Standard”: As the astronomer Carl Sagan famously noted, “Extraordinary claims require extraordinary evidence.” If you claim you have a pet dog, a simple photo is enough. If you claim you have a pet dragon, a photo is no longer sufficient; we require physical, verifiable proof.

5.2 Defeasibility and Open-Mindedness

In Chapter 10.4, we discussed Defeaters. The mark of a truly reasonable person is Defeasibility—the willingness to admit that one’s current knowledge is provisional.

• Fallibilism: This is the philosophical realization that any belief we hold could, in principle, be wrong. It is the opposite of Dogmatism.

• Intellectual Courage: It takes courage to seek out “Undermining Defeaters” for your own most cherished beliefs. A critical thinker doesn’t just wait for evidence to find them; they go looking for the strongest arguments against their own position (a practice known as the Steel Man argument).

5.3 Clifford’s Rule: The Ethics of Belief

In 1877, the mathematician W.K. Clifford wrote a famous essay titled The Ethics of Belief. He argued that believing things without sufficient evidence isn’t just a logical mistake—it’s a moral failure.

• The Shipowner Example: Clifford tells the story of a shipowner who sends a ship full of passengers to sea. He has doubts about the ship’s safety, but he “stifles his doubts” and convinces himself the ship is fine. The ship sinks, and everyone dies.

• The Verdict: Clifford argues the shipowner is guilty of the deaths, even if the ship hadn’t sunk. The sin was the act of believing without evidence.

• Clifford’s Dictum: “It is wrong always, everywhere, and for anyone, to believe anything upon insufficient evidence.”

5.4 James’s Counter: The Will to Believe

William James, a pragmatic philosopher, challenged Clifford. He argued that in some cases—what he called “Genuine Options”—we must believe even when the evidence is not yet in.

• Live, Momentous, and Forced: If a choice is life-changing, cannot be avoided, and the evidence is currently 50/50 (like choosing to marry someone or believing in a higher purpose), James argued that “The Will to Believe” is a rational part of the human experience.

§5 Summary Table: The Ethics of a Reasonable Person