Les principes sont des conventions et des définitions déguisés.
Principles are conventions and definitions in disguise.

Da Vinci was as great a mechanic and inventor as were Newton and his friends. Yet a glance at his notebooks shows us that what fascinated him about nature was its variety, its infinite adaptability, the fitness and the individuality of all its parts. By contrast what made astronomy a pleasure to Newton was its unity, its singleness, its model of a nature in which the diversified parts were mere disguises for the same blank atoms.

EDUCATION, n. That which discloses to the wise and disguises from the foolish their lack of understanding.

From our best qualities come our worst. From our urge to pull together comes our tendency to pull apart. From our devotion to higher good comes our propensity to the foulest atrocities. From out commitment to ideals come our excuse to hate. Since the beginning of history, we have been blinded by evil’s ability to don a selfless disguise. We have failed to see that our finest qualities often lead us to the actions we most abhor—murder, torture, genocide, and war.

Geometrical axioms are neither synthetic a priori conclusions nor experimental facts. They are conventions: our choice, amongst all possible conventions, is guided by experimental facts; but it remains free, and is only limited by the necessity of avoiding all contradiction. ... In other words, axioms of geometry are only definitions in disguise.
That being so what ought one to think of this question: Is the Euclidean Geometry true?
The question is nonsense. One might as well ask whether the metric system is true and the old measures false; whether Cartesian co-ordinates are true and polar co-ordinates false.

Geometry, which should only obey Physics, when united with it sometimes commands it. If it happens that the question which we wish to examine is too complicated for all the elements to be able to enter into the analytical comparison which we wish to make, we separate the more inconvenient [elements], we substitute others for them, less troublesome, but also less real, and we are surprised to arrive, notwithstanding a painful labour, only at a result contradicted by nature; as if after having disguised it, cut it short or altered it, a purely mechanical combination could give it back to us.

I regret that it has been necessary for me in this lecture to administer such a large dose of four-dimensional geometry. I do not apologize, because I am really not responsible for the fact that nature in its most fundamental aspect is four-dimensional. Things are what they are; and it is useless to disguise the fact that “what things are” is often very difficult for our intellects to follow.

Idleness, assuming the specious disguise of industry, will lull to sleep all suspicion of our want of an active exertion of strength.

If mankind is to profit freely from the small and sporadic crop of the heroically gifted it produces, it will have to cultivate the delicate art of handling ideas. Psychology is now able to tell us with reasonable assurance that the most influential obstacle to freedom of thought and to new ideas is fear; and fear which can with inimitable art disguise itself as caution, or sanity, or reasoned skepticism, or on occasion even as courage.

Let no one suppose that the words doctor and patient can disguise from the parties the fact that they are employer and employee.

The process of self-estrangement and its removal underlies all education. The mind must fix its attention upon what is alien to it and penetrate its disguise, making it become familiar. … Wonder is only the first stage of this estrangement. It must be followed by recognition.

There is in every step of an arithmetical or algebraical calculation a real induction, a real inference from facts to facts, and what disguises the induction is simply its comprehensive nature, and the consequent extreme generality of its language.