Alive

Alive is an adjective used to describe organisms or systems that possess life or life-like properties. In everyday language, it contrasts with dead or nonliving and can indicate current activity or vitality. In scientific contexts, the term is often linked to a set of criteria commonly used to distinguish living from nonliving matter, though no single criterion applies universally.

Biology commonly emphasizes several features associated with life: metabolism (energy processing and change), growth, reproduction, response to environmental stimuli, and homeostasis. Over long timescales, life is also characterized by adaptation and evolution. However, edge cases complicate the boundary between alive and non-alive. Viruses, for example, can reproduce but typically do so only inside a host cell and lack independent metabolism. As a result, many scientists consider viruses nonliving outside hosts, while some view them as life-like entities. Other artificial or proposed life-forms, such as protocells or certain autonomous systems, raise questions about whether life requires organic chemistry or if sufficiently complex systems may be considered alive.

Beyond biology, the concept of being alive appears in philosophy, ethics, law, and language. It is used to discuss the status of nonhuman entities, to describe life-like systems such as autonomous machines, and as an intensifier in expressions like “alive and well.” The term thus spans empirical definitions, theoretical debate, and everyday usage.