For the most part, everything falls into one of two categories: It’s either alive, or it isn’t. Ever since scientists have been aware of the existence of viruses, they’ve been unable to successfully determine which of these two very distinct groups viruses belong to. Originally, viruses were thought to be alive. The scientists that discovered viruses saw them as organisms that could spread and multiply, suggesting that they were very clearly alive. By the 1930s, however, researchers from the Rockefeller University were finally able to get a look into what was going on inside a virus. Since it didn’t have any metabolic functions, they decided that it wasn’t alive.But it’s far from clear, as further research by the same team discovered that a virus also exhibits one of the key components of life: reproduction. It not only makes more of itself but creates more proteins and internal chemical structures. Viruses have also been known to change over time, evolve, and carry on processes like repairing damage done to them. All this seems to indicate they’re alive, unless nonliving organisms are also capable of evolution, which seems like a pretty odd thing to even suggest.
Viruses are also unable to carry on these processes outside of a living host, leading some to suggest that they’re functioning on something along the lines of life borrowed from another organism—but that doesn’t make the answer any more clear.