Begin with the direct cause and proceed up the chain. Explaining actions in terms of one's reasons or motives. The component of a behavioral explanation entails some antecedent event or situation, and a dependable psychological generality. Like physical explanations, psychological explanations are only as good as the psychological theory on which they based. Explanation or an object or occurrence in terms of its purpose or function.
Physical explanations look back in time.
Antibodies attach foreign bodies to prevent infection. Physical explanations look back in time. Functional explanations are not bound by this restriction. If X is more familiar than Y, then we may be able to communicate information about Y by comparing it to X, provided the two have singificant features in common. For example, we may explain to a European how American football is played by comparing it to rugby, a European game that has many features similar to American football.