# Quote — Henri Poincaré, The Value of Science

> We have not a direct intuition of simultaneity, nor of the equality of two durations. If we think we have this intuition, this is an illusion. We replace it by the aid of certain rules which we apply almost always without taking count of them.
>
> ...We ...choose these rules, not because they are true, but because they are the most convenient, and we may recapitulate them as follows: "The simultaneity of two events, or the order of their succession, the equality of two durations, are to be so defined that the enunciation of the natural laws may be as simple as possible. In other words, all these rules, all these definitions, are only the fruit of an unconscious opportunism."

- Author: [Henri Poincaré](https://www.leafyquotes.com/henri-poincare.md)
- Book: [The Value of Science](https://www.leafyquotes.com/henri-poincare/the-value-of-science.md)
- Source: [Wikiquote](https://en.wikiquote.org/wiki/Henri_Poincar%C3%A9#Ch._2:_The_Measure_of_Time) ([CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/))
- Topics: [science](https://www.leafyquotes.com/topics/science.md), [time](https://www.leafyquotes.com/topics/time.md)
- Quote page: https://www.leafyquotes.com/henri-poincare/the-value-of-science/we-have-not-a

## More from this book

> Does the harmony the human intelligence thinks it discovers in nature exist outside of this intelligence? No, beyond doubt, a reality completely independent of the mind which conceives it, sees or feels it, is an impossibility. A world as exterior as that, even if it existed, would for us be forever inaccessible.

[Quote page](https://www.leafyquotes.com/henri-poincare/the-value-of-science/does-the-harmony.md)

> Time and Space … It is not nature which imposes them upon us, it is we who impose them upon nature because we find them convenient.

[Quote page](https://www.leafyquotes.com/henri-poincare/the-value-of-science/time-and-space.md)

> The advance of science is not comparable to the changes of a city, where old edifices are pitilessly torn down to give place to new, but to the continuous evolution of zoologic types which develop ceaselessly and end by becoming unrecognizable to the common sight, but where an expert eye finds always traces of the prior work of the centuries past. One must not think then that the old-fashioned theories have been sterile or vain.

[Quote page](https://www.leafyquotes.com/henri-poincare/the-value-of-science/the-advance-of-science.md)