LessWrong: 'Unrealistic Hypothetical' Objection Is a Logical Fallacy

In a recent LessWrong post, the author dismantles the common objection 'this hypothetical is unrealistic' as a valid critique. The argument centers on the nature of hypotheticals: they are explicitly unreal scenarios used to test principles. If one rejects all unreal premises, then every 'if' statement—including those about past events or future plans—becomes invalid. Counterfactual reasoning, the foundation of planning and causal understanding, would collapse. The post further argues that even granting a steelman of impossibility (i.e., 'X cannot happen'), the set of impossible conditions is far smaller than improbable ones, and many unrealistic scenarios are logically or physically possible (e.g., a tennis match with Christopher Walken).

To illustrate why contrived cases matter, the author presents a syllogism: if murder is wrong universally, then murder in a 'distant marshmallow galaxy' or killing a dying man to save 1000 lives must also be wrong. If the conclusion seems false, the universal principle must be qualified. Thus, dismissing hypotheticals as 'unrealistic' evades the necessary testing of ethical or rational principles. The post concludes that engaging with absurd scenarios is essential for rigorous thinking—our principles must account for all instances, not just convenient ones.