Final answer:
The difference between something happening for no reason and something being necessary is explained by causality and the presence or absence of a cause.
Step-by-step explanation:
The difference between something happening for no reason and something being necessary lies in causality and the presence or absence of a cause. When something happens for no reason, it means that there is no identifiable cause for that event. On the other hand, when something is necessary, it means that it must happen due to a specific cause or condition. For example, if a glass falls and breaks for no reason, there is no known cause for the event. However, if the glass falls and breaks because it was pushed off the table, then the falling and breaking of the glass is necessary due to the external force exerted on it.
When considering human behavior, the notion of necessity can also involve internal forces such as motives, purposes, or desires that propel a person to act in certain ways. These actions are contrasted with behaviors that seem to have no reason, or are not tied to a specific goal or end.