Importance is a property of entities that matter or make a difference. For example, World War II was an important event and Albert Einstein was an important person because of how they affected the world. There are disagreements in the academic literature about what type of difference is required. According to the causal impact view, something is important if it has a big causal impact on the world. This view is rejected by various theorists, who insist that an additional aspect is required: that the impact in question makes a value difference. This is often understood in terms of how the important thing affects the well-being of people. So in this view, World War II was important, not just because it brought about many wide-ranging changes but because these changes had severe negative impacts on the well-being of the people involved. The difference in question is usually understood counterfactually as the contrast between how the world is and how the world would have been without the existence of the important entity. It is often argued that importance claims are context- or domain-dependent. This means that they either explicitly or implicitly assume a certain domain in relation to which something matters. For example, studying for an exam is important in the context of academic success but not in the context of world history. Importance comes in degrees: to be important usually means to matter more within the domain in question than most of the other entities within this domain.
The term "importance" is often used in overlapping ways with various related terms, such as "meaningfulness", "value", and "caring". Theorists frequently try to elucidate these terms by comparing them to show what they have in common and how they differ. A meaningful life is usually also important in some sense. But meaningfulness has additional requirements: life should be guided by the agent's intention and directed at realizing some form of higher purpose. In some contexts, to say that something is important means the same as saying that it is valuable. More generally, however, importance refers not to value itself but to a value difference. This difference may also be negative: some events are important because they have very bad consequences. Importance is often treated as an objective feature in contrast to the subjective attitude of caring about something or ascribing importance to it. Ideally, the two overlap: people subjectively care about objectively important things. Nonetheless, the two may come apart when people care about unimportant things or fail to care about important things. Some theorists distinguish between instrumental importance relative to a specific goal in contrast to a form of importance based on intrinsic or final value. A closely related distinction is between importance relative to someone and absolute or unrestricted importance.
The concept of importance is central to numerous fields and issues. Many people desire to be important or to lead an important life. It has been argued that this is not always a good goal since it can also be realized negatively: by causing a lot of harm and thereby making an important but negative value difference. Common desires that are closely related include wanting power, wealth, and fame. In the realm of ethics, the importance of something often determines how one should act towards this thing, for example, by paying attention to it or by protecting it. In this regard, importance is a normative property, meaning that importance claims constitute reasons for actions, emotions, and other attitudes. On a psychological level, considerations of the relative importance of the aspects of a situation help the individual simplify its complexity by only focusing on its most significant features. A central discussion in the context of the meaning of life concerns the question of whether human life is important on the cosmic level. Nihilists and absurdists usually give a negative response to this question. This pessimistic outlook can in some cases cause an existential crisis. In the field of artificial intelligence, implementing artificial reasoning to assess the importance of information poses a significant challenge when trying to deal with the complexity of real-world situations.