The basic tenet underlying all of Buber's philosophy is the contention that man has two modes available to him through which he can engage the world. The first mode (the mode of I–It) is the mode of experience. In experience, we engage the world as an objective observer rather than as a participant, and we gather data through the senses and organize that data in such a way that it can be utilized by reason. Experience is the mode of science and philosophy, the mode through which we come to know things intellectually, and to put things to use for us. Western culture, Buber claims, has generally come to think that this is the only mode available to human beings for engaging the world. We tend to ignore the other mode, which is more vital to our existence as human beings.

This second mode that we often ignore is what he calls the mode of encounter. In encounter (the mode of I–You), we participate in a relationship with the object encountered. Both the encountering I and the encountered You are transformed by the relation between them. Whereas experience is entered into with only part of one's self (the data-collecting, analyzing, theorizing part), one enters encounter with one's whole self. Whereas experience involves distance between the I and the It (i.e. the distance between subject and object) relation involves no such distance. And whereas the I of experience views the It only as a collection of qualities and quantities, the I of encounter sees the You as much more than that; the I of encounter sees the entire world through the You for as long as the encounter lasts.

Most encounters, unfortunately, cannot last very long. Encounters with inanimate objects of nature, with animals, and with other human beings are necessarily fleeting. Eventually we come to reflect on the You, to see it for its various qualities, to analyze it. Once we do this, the You dissolves into an It, and we are back in the realm of experience. It is only encounter with the eternal You, God, that is lasting and ultimately fulfilling.

Though Buber's aim is to get us to recognize that the mode of encounter is available to us and to help us open ourselves up to it, he does not believe that we should ignore the mode of experience. The mode of experience is necessary to our survival. It is through experience that we come to see an order in the world which we then use to obtain the necessary elements of survival. The realm of science cannot be discarded; but it is also not sufficient for our existence as human beings.