Anyone who conducts an argument by appealing to authority is not using his intelligence; he is just using his memory.
Common Sense is that which judges the things given to it by other senses.
I have been impressed with the urgency of doing. Knowing is not enough; we must apply. Being willing is not enough; we must do.
For once you have tasted flight you will walk the earth with your eyes turned skywards, for there you have been and there you will long to return.
Although nature commences with reason and ends in experience it is necessary for us to do the opposite, that is to commence with experience and from this to proceed to investigate the reason.
As a well-spent day brings happy sleep, so a life well spent brings happy death.
Every now and then go away, have a little relaxation, for when you come back to your work your judgment will be surer. Go some distance away because then the work appears smaller and more of it can be taken in at a glance and a lack of harmony and proportion is more readily seen.
Experience does not err. Only your judgments err by expecting from her what is not in her power.
He who loves practice without theory is like the sailor who boards ship without a rudder and compass and never knows where he may cast.
Human subtelty will never devise an invention more beautiful, more simple or more direct than does Nature, because in her inventions, nothing is lacking and nothing is superfluous.
I have offended God and mankind because my work didn't reach the quality it should have.