The Principle of Optimism

Definition

Deutsch states the principle plainly: "All evils are caused by insufficient knowledge." Nothing permitted by the laws of physics is forbidden to us forever — only not-yet-known. This is not a prediction that things will turn out well; it is a stance that problems are always solvable in principle, and a rejection of "prophecy" — the pretense of knowing the content of knowledge not yet created. Deutsch distinguishes rational prediction (what follows from a good existing explanation) from prophecy (claims about what unknown future knowledge will bring), and argues both blind optimism and blind pessimism (the "precautionary principle") are prophetic in this illegitimate sense.

In the Book

Deutsch works through a series of historical failed prophecies: physicist Albert Michelson's 1894 claim that physics was essentially complete, just before relativity and quantum theory overturned it; Thomas Malthus's 1798 prediction of inevitable mass starvation, which correctly forecast exponential population growth but completely missed the even-faster growth in food production that new knowledge would enable; and Martin Rees's argument (in Our Final Century) that civilization has only a 50% chance of surviving the twenty-first century, which Deutsch rebuts by noting that the future of civilization, unlike a game of Russian roulette, depends on choices, not fixed odds. He tells the folk story of the prisoner who bargains a year's reprieve by promising to teach the king's horse to talk — "a lot can happen in a year... the horse might talk" — as an illustration of optimism as a stance toward the inconceivable, not a probability estimate. He applies the same logic to Kennedy's 1962 decision to go to the moon "not because it is easy, but because it is hard": hardness, for an optimist, is a reason to engage with a problem, since progress means creating knowledge that could not have been foreseen in advance.

Why It Matters

This separates two things that get routinely conflated in planning and forecasting: legitimate prediction from existing good explanations, versus illegitimate prophecy about knowledge that doesn't exist yet. It gives a principled reason to distrust both confident doom-forecasting and complacent reassurance about any long-range future — climate, technology, markets, institutions — while still endorsing rigorous, falsifiable predictions from explanations that are actually in hand. It reframes "hard problems" as the ones worth choosing precisely because solving them requires (and produces) new knowledge.