"I exist, therefore I'll think."
"Devotion to the truth is the hallmark of morality; there is no greater, nobler, more heroic form of devotion than the act of a man who assumes the responsibility of thinking."
"Man’s mind is his basic tool of survival. Life is given to him, survival is not. His body is given to him, its sustenance is not. His mind is given to him, its content is not. To remain alive, he must act, and before he can act he must know the nature and purpose of his action. He cannot obtain his food without a knowledge of food and of the way to obtain it. He cannot dig a ditch – or build a cyclotron – without a knowledge of his aim and of the means to achieve it. To remain alive, he must think.
But to think is an act of choice. [...] In any hour and issue of your life, you are free to think or to evade that effort. But you are not free to escape from your nature, from the fact that reason is your means of survival – so that for you, who are a human being, the question ‘to be or not to be’ is the question ‘to think or not to think’."
"Man must obtain his knowledge and choose his actions by a process of thinking, which nature will not force him to perform."