If you have an idea

"If you have an apple and I have an apple and we
 exchange apples then you and I will still each have one
 apple. But if you have an idea and I have an idea and we
 exchange these ideas, then each of us will have two
 ideas." - George Bernard Shaw

Ideas and stars

"Ideals are like the stars: we never reach them, but like the mariners of the sea, we chart our course by them." - Carl Schurz