Mathematics is the only true metaphysics.

I need scarcely say that the beginning and maintenance of life on earth is absolutely and infinitely beyond the range of all sound speculation in dynamical science. The only contribution of dynamics to theoretical biology is absolute negation of automatic commencement or automatic maintenance of life.

Christianity without the cross is nothing. The cross was the fitting close of a life of rejection, scorn and defeat. But in no true sense have these things ceased or changed. Jesus is still He whom man despiseth, and the rejected of men. The world has never admired Jesus, for moral courage is yet needed in every one of its high places by him who would "confess" Christ. The "offense" of the cross, therefore, has led men in all ages to endeavor to be rid of it, and to deny that it is the power of God in the world.

Fourier is a mathematical poem.

Heavier-than-air flying machines are impossible.

Simplification of modes of proof is not merely an indication of advance in our knowledge of a subject, but is also the surest guarantee of readiness for farther progress.

If you can not measure it, you can not improve it.