But the particular event, the particular complaint for which the patient comes to us, is woven not merely into one chain of evidence, but into several. Let us carry out the metaphor of the chain. We must imagine many chains woven into one another like the chain-armor of the mediæval knight. Each link is a fact. But many chains of facts are interwoven in the history of one single patient. First there is the chain of medical evidence, the links (or symptoms) leading up to a diagnosis; second, the chain of social evidence, which we try to classify on our social history card. Third, we must trace the links in the chain of relationship with other people, other members of the family, with friends and fellow workers or schoolmates. Finally, the chain of heredity, of which we cannot make much at present except in relation to tuberculosis and mental disease or mental deficiency. But these studies of heredity in its bearing on character are going to be more important as the science of social work develops. Our first attempt, then, after determining the "presenting symptom," is to find out by a series of questions _how this symptom is linked up into a tissue composed of many chains of facts_. Our next task which is usually difficult, and frequently impossible, is to find out why this great tissue of evidence issues just now in one particular "presenting symptom." Why did the patient come to us to-day? This question is often impossible to answer because the patient does not know, though he may think he knows. Nevertheless, the social worker must try to find out. Often it is not until we have known and liked a person for days or weeks that we find out why he came to us at this particular time. Yet the answer to this question may be the most important thing that we can find out. For two reasons it is important; first, because it furnishes the clue to all our later investigation and assistance in this case; secondly, because it may show that the individual's complaints are not of any significance at all.