Spinoza‘s conatus is the near equivalent of Tillich’s courage to be. Being is not something that just is; it must constantly strive to affirm itself against the threats posed by nonbeing. For both Spinoza and Tillich, this continuous affirmation of being is also the essence of each individual person. It is related to both Augustine‘s "restlessness" and Nietzsche‘s "will to power." From the tiniest insect to the entire cosmos, that which is must strive to maintain itself in being. For Tillich, this endless struggle is not something to be lamented. Without it life would be inert, not real life at all.
Hamlet‘s "To be or not to be" is indeed the question. It is every-one‘s question, and it is also the one that underlies all the questions asked by the various academic specialties. This explains why Tillich believed that an analysis of courage could help bridge the between philosophy, science, literature, and theology.
To today‘s reader, however, who rarely worries about bridging the chasm between disciplines but does muse, at least on occasion, about his or her own existence, this may all sound quaintly theoretical. For Tillich it is not. When he recalls that the word "courage" derives from the French word for heart, he also reminds the reader that the "heart" symbolizes far more than just the seat ofemotions. It has meant, and still means, the vital center of reality. - P14