It is often said that experiments should be made without preconceived ideas. That is impossible. Not only would it make every experiment fruitless, b… - Henri Poincaré

For an aggregate of sensations to have become a remembrance capable of classification in time, it must have ceased to be actual, we must have lost the sense of its infinite complexity, otherwise it would have remained present. It must, so to speak, have crystallized around a center of associations of ideas which will be a sort of label. It is only when they have lost all life that we can classify our memories in time as a botanist arranges dried flowers in his herbarium.

La recherche de la vérité doit être le but de notre activité ; c'est la seule fin qui soit digne d'elle. Sans doute nous devons d'abord nous efforcer de soulager les souffrances humaines, mais pourquoi ?

The axioms of geometry, therefore, are neither synthetic a priori judgments nor experimental facts.
They are conventions; our choice among all possible conventions is guided by experimental facts; but it remains free and is limited only by the necessity of avoiding all contradiction. . . .
In other words, the axioms of geometry (I do not speak of those of arithmetic) are merely disguised definitions.
Then what are we to think of that question: Is the Euclidean geometry true?
It has no meaning.
As well ask whether the metric system is true and the old measures false.