
Everyone knows what a curve is, until he has studied enough mathematics to become confused through the countless number of possible exceptions.
Felix Klein 
Thus, in a sense, mathematics has been most advanced by those who distinguished themselves by intuition rather than by rigorous proofs.
Felix Klein

The developing science departs at the same time more and more from its original scope and purpose and threatens to sacrifice its earlier unity and split into diverse branches.
Felix Klein 
The greatest mathematicians, as Archimedes, Newton, and Gauss, always united theory and applications in equal measure.
Felix Klein 
Every one who understands the subject will agree that even the basis on which the scientific explanation of nature rests is intelligible only to those who have learned at least the elements of the differential and integral calculus, as well as analytical geometry.
Felix Klein 
Projective geometry has opened up for us with the greatest facility new territories in our science, and has rightly been called the royal road to our particular field of knowledge.
Felix Klein 
The presentation of mathematics in schools should be psychological and not systematic. The teacher, so to speak, should be a diplomat. He must take account of the psychic processes in the boy in order to grip his interest, and he will succeed only if he presents things in a form intuitively comprehensible. A more abstract presentation is only possible in the upper classes.
Felix Klein 
It is well known that the central problem of the whole of modern mathematics is the study of transcendental functions defined by differential equations.
Felix Klein

Regarding the fundamental investigations of mathematics, there is no final ending ... no first beginning.
Felix Klein 
Mathematics in general is fundamentally the science of selfevident things.
Felix Klein 
Among mathematicians in general, three main categories may be distinguished; and perhaps the names logicians, formalists, and intuitionists may serve to characterize them.
Felix Klein 
The teacher manages to get along still with the cumbersome algebraic analysis, in spite of its difficulties and imperfections, and avoids the smooth infinitesimal calculus, although the eighteenth century shyness toward it had long lost all point.
Felix Klein