The claim links two developments: the emergence of the individual thinker as a source of knowledge, and the rise of periods of sustained scientific advance. On this reading they did not merely coincide but depend on one another, because science proceeds by challenging accepted accounts, which requires people willing to disagree with established authority.

The word inseparable makes the relationship structural rather than accidental. Where conclusions are dictated by doctrine or the state, the mechanism of correction is disabled: findings cannot be tested against evidence if certain findings are not permitted. Discovery is presented as an activity that individuals undertake, even when the work itself is collective.

Full quotation

“This leads to the paradoxical situation that a person who devotes all his strength to objective matters will develop, from a social point of view, into an extreme individualist who, at least in principle, has faith in nothing but his own judgment. It is quite possible to assert that intellectual individualism and scientific eras emerged simultaneously in history and have remained inseparable ever since.”