The mode of I–You is the mode of encounter or relation. We can enter into encounter with nature (both plant and animal), with other human beings, and with spiritual beings (such as God). Since this mode is not quite as simple to grasp as experience, it is best to break it down into its component characteristics, and to treat each separately: The most important aspect of encounter is that it requires us to be active participants rather than objective observers. We must enter into encounter with our entire being, and allow ourselves to be changed by it. Encounter, Buber tells us, is a moment of reciprocity, in which both the I and the You are transformed. This is why he calls relation dialogical, or conversational: much like a conversation or dialogue, encounter takes place between the two participants rather than inside one or the other, and it involves calling out toward a You and expecting a response. Experience, on the other hand, takes place entirely inside the I. The I observes, the I analyzes, all inside its own head. When the I of experience says "It", it is not seeking an answer from its object.
The notion of mutual transformation between the I and the You in the moment of encounter is most easily understood when we consider an encounter between an artist and his or her creation (Buber considers this a paradigm example of encounter). It is easy to see how both the art and the artist are changed by the creative process: the art acquires form and comes into being; the artist goes through various psychological, emotional, and mental transformations as a result of the process.
The second key feature of encounter is that, whereas in experience the I sees the It merely as the sum of its qualities, in encounter the I sees the You as much more than that sum. One encounters the whole You in the full manifold of its existence. Instead of viewing the You as a point in space and time, the I of encounter views all of space and time, the entire universe, through the You. In a sense, then, the You becomes the Universe for the encountering I.
Part of what enables the I to approach the You in this way (i.e. in its entirety of being) is the fact that relation is immediate or unmediated. We enter encounter without any relevant concepts, any prior knowledge, any greed, desires, or anticipation of what the You will be like. There us nothing mental separating the I from the You.
Encounter is also what Buber calls "pure present". Encounter is where the present takes place, whereas experience deals only with past. Presumably, this is because in encounter both the You and the I are removed from space and time. Seen apart from the flow of time, the You becomes enduring, eternal, and our relation with the You can occupy the present without continually falling into the past. In experience, on the other hand, we see the object as a point in time, and since every moment in time is always ending, we are never really in the present so long as we are in the realm of experience.
Nevertheless, though encounter is pure present, it is always necessarily fleeting. Any You, except the eternal You (God), will inevitably degenerate back into an It as soon as we become aware of the encounter, and begin to reflect on it.
Buber finds a place for religion outside of rationality in the mode of encounter. He believes that throughout the scientific age the critics of religion have shown correctly that God cannot really fit within the world so long as we are trying to get at the world in the typical way. That is, he recognizes that science and reason can never get us to God, because "it is not as if God could be inferred from anything" (III.4).
God cannot be inferred from anything because the world is causally closed: we never have to appeal to anything outside of the physical world in order to explain a physical phenomenon. All explanations for physical events and states can be given in the form of other physical events and states. Thus, we can never find God through experience, for within the realm of experience we come to know things only by gathering sensory data, and analyzing this data with our reason.
It is not irreligious to claim that the physical world is causally closed (after all, this is certainly the most perfect sort of order that God could have imposed on the world) but if we cannot get at God the way we get at everything else (through reasoning from the data), where can the justification for believing in God's existence possibly come from? Buber says that it comes through encounter. In this mode of engaging we do not gather sense data to be analyzed with reason, rather we simply enter into a relationship with the whole being of whatever it is we are relating to.
This key concept of encounter is one of those notions which Buber tells us can never be made entirely explicit through language. The whole point of encounter is that it cannot be analyzed, described, or reduced down to qualities in space and time. Naturally, this makes it very difficult for Buber to convey the subtleties of the concept to his readers. What does it mean, for instance, to say that the I views the You as more than the sum of its qualities, or in its full being? What specifically is this "more" that we are seeing? Buber cannot tell us, because any aspect of the You that could be described would have to be those qualities that we latch onto in experience. The "something more", by its very nature, cannot be described or analyzed.
The same trouble arises for other aspects of the account: what does it mean to say that in encounter we view the entire Universe through the You? Again, we cannot have more than a vague sense of what this might mean, because Buber cannot really describe encounter to us; we must go through it ourselves in order to know what it is like.
But these difficulties should not make us despair of coming to an understanding of the mode of encounter. As we will see in the next section, much can be gained by comparing encounter to the state of being in love, and other questions can be answered with a little patience and guesswork. For instance, Buber says that we are changed by encounter, and this naturally leads to questions about the nature of this change. Are we changed permanently or only so long as the encounter lasts? Are we spiritually changed, or emotionally, or physically, or mentally? In the case of transformation as a result of divine revelation, Buber is clear about the nature of this change: the change is permanent, and it involves our very ability to encounter. We are transformed in such a way that we can say "You" to the entire world; we suddenly feel a loving responsibility toward everyone and everything.
Encounters with human beings, at least, seem to have very similar consequences as the encounter with God. When describing the relation of man to man Buber says, "now one can act, help, heal, educate, raise, redeem" (I.19). The transformation in the case of relation to man, it seems clear, is also the growth of a loving responsibility, but only toward the You of the relation, rather than toward the whole world.
But what about the relation to nature? Unfortunately, here we hit the old frustrating wall of indescribability. Buber suggests that we let this type of transformation "remain mysterious" (I.19). Presumably, this means that encounter with nature does not result in the same sort of transformation (i.e. we do not develop a loving responsibility toward the cat or the tree), but rather in a different sort of transformation which cannot be easily put into words. The claim that encounter is unmediated is best understood if we draw an analogy between the two modes of engaging the world and two different ways of listening. There are two ways that someone can listen to another human being: first, the listener can approach the conversation armed with background knowledge about the speaker and expectations about what the speaker will say. If you approach a conversation in this way, you will hear only what makes sense to you given your knowledge and expectations. The other way to listen is to clear oneself of all prior knowledge and expectations, and simply open oneself up to the words being spoken. It is only if you listen in this way, that you enable yourself to truly hear everything that the other person is saying. This second way of listening is like unmediated relation. By approaching the encounter unmediated, we open ourselves up to come into contact with anything that the You has to offer, with the fullness of the You's being.