There are three principal means of acquiring knowledge... observation of nature, reflection, and experimentation. Observation collects facts; reflection combines them; experimentation verifies the result of that combination.
Some suggestions for you :
Doctors are always working to preserve our health and cooks to destroy it, but the latter are the more often successful.
Patriotism is an ephemeral motive that scarcely ever outlasts the particular threat to society that aroused it.
It is said that desire is a product of the will, but the converse is in fact true: will is a product of desire.
The philosopher has never killed any priests, whereas the priest has killed a great many philosophers.
Although a man may wear fine clothing, if he lives peacefully; and is good, self-possessed, has faith and is pure; and if he does not hurt any living being, he is a holy man.
Power acquired by violence is only a usurpation, and lasts only as long as the force of him who commands prevails over that of those who obey.
Genius is present in every age, but the men carrying it within them remain benumbed unless extraordinary events occur to heat up and melt the mass so that it flows forth.
To attempt the destruction of our passions is the height of folly. What a noble aim is that of the zealot who tortures himself like a madman in order to desire nothing, love nothing, feel nothing, and who, if he succeeded, would end up a complete monster!
Sentences are like sharp nails, which force truth upon our memories.
Gaiety is a quality of ordinary men. Genius always presupposes some disorder in the machine.