Variation must be taken as random until there is positive evidence to the contrary.

- Harold Jeffreys

The real difficulty about volcanism is not to see how it can start, but how it can stop.

- Harold Jeffreys

There are some current 'theories' that, when divested of begged questions, reduce to the non-controversial statement, 'Here are some facts and there …

- Harold Jeffreys

What the use of P [the significance level] implies, therefore, is that a hypothesis that may be true may be rejected because it has not predicted obs…

- Harold Jeffreys

All suggested accounts of the origin of the solar system are subject to serious objections. The conclusion in the present state of the subject would …

- Harold Jeffreys

A formal and consistent theory of inductive processes cannot represent the operation of every human mind in detail; it will represent an ideal mind, …

- Harold Jeffreys

An observation, strictly, is only a sensation. Nobody means that we should reject everything but sensations. But as soon as we go beyond sensations w…

- Harold Jeffreys

We have to come back to something like ordinary language after all when we want to talk "about" mathematics!

- Harold Jeffreys