Quotes from David Deutsch

Rejecting authority in regard to knowledge was not just a matter of abstract analysis. It was a necessary condition for progress, because, before the Enlightenment, it was generally believed that everything important that was knowable had already been discovered, and was enshrined in authoritative sources such as ancient writings and traditional assumptions. Some of those sources did contain some genuine knowledge, but it was entrenched in the form of dogmas along with many falsehoods

People are significant in the cosmic scheme of things; and The Earth's biosphere is incapable of supporting human life.

They can be understood only by being explained. Fortunately, our best theories embody deep explanations as well as accurate predictions.

Scientific theories explain the objects and phenomena of our experience in terms of an underlying reality which we do not experience directly. But the ability of a theory to explain what we experience is not its most valuable attribute. Its most valuable attribute is that it explains the fabric of reality itself.

To say that prediction is the purpose of a scientific theory is to confuse means with ends. It is like saying that the purpose of a spaceship is to burn fuel. In fact, burning fuel is only one of many things a spaceship has to do to accomplish its real purpose, which is to transport its payload from one point in space to another. Passing experimental tests is only one of many things a theory has to do to achieve the real purpose of science, which is to explain the world.

For example, you cannot predict what numbers will come up on a fair (i.e. unbiased) roulette wheel. But if you understand what it is in the wheel's design and operation that makes it fair, then you can explain why predicting the numbers is impossible.

A theory may be superseded by a new theory which explains more, and is more accurate, but is also easier to understand, in which case the old theory becomes redundant, and we gain more understanding while needing to learn less than before. That is what happened when Nicolaus Copernicus's theory of the Earth travelling round the Sun superseded the complex Ptolemaic system which had placed the Earth at the centre of the universe.

That is to say, every putative physical transformation, to be performed in a given time with given resources or under any other conditions, is either – impossible because it is forbidden by the laws of nature; or – achievable, given the right knowledge.

a rational political system makes it as easy as possible to detect, and persuade others, that a leader or policy is bad, and to remove

We understand the fabric of reality only by understanding theories that explain it. And since they explain more than we are immediately aware of, we can understand more than we are immediately aware that we understand.

This is the cosmic significance of explanatory knowledge – and hence of people, whom I shall henceforward define as entities that can create explanatory knowledge.

Before 1945, no human being had ever observed a nuclear-fission (atomic-bomb) explosion; there may never have been one in the history of the universe.

Solipsism, the theory that only one mind exists and that what appears to be external reality is only a dream taking place in that mind, cannot be logically disproved.

the Principle of Mediocrity opposes the pre-Enlightenment arrogance of believing ourselves significant in the world; the Spaceship Earth metaphor opposes the Enlightenment arrogance of aspiring to control the world.

No man ever steps in the same river twice, for it is not the same river and he is not the same man.

Even a typical star converts millions of tonnes of mass into energy every second, with each gram releasing as much energy as an atom bomb.

Bad philosophy before the Enlightenment was typically of the because-I-say-so variety. When the Enlightenment liberated philosophy and science, they both began to make progress, and increasingly there was good philosophy. But, paradoxically, bad philosophy became worse.

the assumption that progress in a hypothetical rapacious civilization is limited by raw materials rather than by knowledge.

The idea that there could be beings that are to us as we are to animals is a belief in the supernatural.

Prediction – even perfect, universal prediction – is simply no substitute for explanation.

one thing that all conceptions of the Enlightenment agree on is that it was a rebellion, and specifically a rebellion against authority in regard to knowledge.

on learning how to reject their authority. This is why the Royal Society (one of the earliest scientific academies, founded in London in 1660) took as its motto 'Nullius in verba', which means something like 'Take no one's word for it.

What was needed for the sustained, rapid growth of knowledge was a tradition of criticism. Before the Enlightenment, that was a very rare sort of tradition: usually the whole point of a tradition was to keep things the same.

After all, computers play chess mindlessly – by exhaustively searching the consequences of all possible moves – but humans achieve a similar-looking functionality in a completely different way, by creative and enjoyable thought.