Social Psychology/Human Relations
Understanding the essence of People and their interactions.... 
We as people interact on a physical basis on many levels, firstly through our body language, secondly through our tone of voice and finally through the content of our words spoken, surprisingly this last level offers the least amount of information to the other person in the communication process whom is receiving the message. This is because when people communicate they are expressing not only through their mental conscious thoughts but are also being influenced by their sub conscious mind, consequently communicating other messages to the receiver in the form of body language. As a result of this, the perceptive receiver may hear the words being spoken by the communicator but may also get an understanding of the feelings behind the messages, these messages may contradict the message from the words, consequently adding more understanding to the interactions. For example, a person may say to you "I feel comfortable around you" and at the same time may be crossing his/her arms possibly showing the defensive body posture. The receiver in this situation, if aware of these messages, would obviously have to consider the sincerity of the other's words. Finally, careful listening needs to be exercised when listening to the words, as the way that words are expressed can add many different messages. For example, "Hi." in a low-toned, brief manner could indicate that the communicator is feeling tired or down, whereas a longer, higher-toned "Hi!" could mean happiness or happy to see you.
Therefore, to ensure a full understanding of how each interaction between yourself and any fellow person in this world is achieved, as long as you both speak the same language of course, you need to actively pay attention and consider the three essential levels. It must also be noted that there are other factors which affect a person's ability to understand all of these messages. Firstly, our perception--how each individual see things in this world--can limit understanding. Perception is developed through a person's lifetime through their life experiences; one is more likely to perceive an event based on what they have experienced in the past, making a connection in understanding from what they have already understood/experienced about the event. This can have limiting effects on one's ability to understand, as a person can get the feeling of confidence that they fully understand the situation when in fact they may miss important messages being communicated through their interactions. An example of this would be early judgements on the communicator's behaviour and motives.