Astronomy is useful because it raises us above ourselves; it is useful because it is grand; .... It shows us how small is man's body, how great his mind, since his intelligence can embrace the whole of this dazzling immensity, where his body is only an obscure point, and enjoy its silent harmony.

The scientist does not study nature because it is useful; he studies it because he delights in it, and he delights in it because it is beautiful.

Mathematicians do not deal in objects, but in relations between objects; thus, they are free to replace some objects by others so long as the relations remain unchanged. Content to them is irrelevant: they are interested in form only.

Geometry is the art of correct reasoning from incorrectly drawn figures.

If we ought not to fear mortal truth, still less should we dread scientific truth. In the first place it can not conflict with ethics? But if science is feared, it is above all because it can give no happiness? Man, then, can not be happy through science but today he can much less be happy without it.

Science is built up with facts, as a house is with stones. But a collection of facts is no more a science than a heap of stones is a house.

Doubt everything or believe everything: these are two equally convenient strategies. With either we dispense with the need for reflection.