I and Thou by Martin Buber (1923)

There is a difference between saying 'You' to someone and saying 'It,' and Martin Buber built a whole philosophy on it. To speak 'Thou' is to stand before another in full presence, holding nothing back, so that a person, a tree, even God stops being a thing you observe and becomes a whole world that meets you back. To speak 'It' is to step away and describe, measure, use. These are not passing moods but two ways of having a self, and Buber's quiet, shattering claim is that the I who says 'Thou' is not the same I who says 'It.' He writes in prose so compressed it reads like scripture, mourning a modern life that has let usefulness swallow encounter, until even the people we love thin into functions. God he calls the eternal Thou, the one relation that can never curdle into an object. Every other Thou, he admits, will. _I and Thou_ lives in the brief warm interval before it does, and it will leave you desperate to keep one bond from going cold.