We are not merely individuals. This is a very important truth that we have to learn when we study anything. If we are, in fact, isolated individuals, speaking strictly from the point of view of the logical definition of the word 'individual', there would be no communication between one individual and another. The scientific definition of the term 'individual' implies self-affirmation and a segregation of the selfhood of the person to such an extent that there is a complete demarcation of one individual from the other. If such a difference of such a marked nature were to be present in the individuality of the human being, you could very well imagine the consequence. There would be no communication between individuals, merely because of the fact that they are 'individuals'. The isolation that is implied in the affirmation of the self is a bar to any kind of amiable relationship among persons. But what is it that we are aiming at in public life, if not social harmony, peace as we call it, in public life and in our existence as units of society as well as the international system. Thus, it would come to light that Yoga is not merely a personal affair, it is not the business of the individual as a self centred something, but it has a connotation with a wider dimension, with its connections extending through its tentacles to the far reaches of all creation, as it were. The practice of Yoga is, really, the practice of the art of living. It is not any mystical doctrine of any section of people, it is not a creed or a cult but a system of living, a system which is of such a universal character that no one can afford to forgo it. It is the science of the basic structure of the human individual in its relationships with all that exists, whether in Society or in Nature outside; and from this point of view we may say that the practice of Yoga is the practice of the art or the science of public living in its principal sense. For our purpose we may classify human life into four broad aspects, though there can be minor details of this classification.