If you mean "life" or "death" are merely mental categories that don't have existence in reality, then saying "this is alive" or "this is dead", or "this is close to life" or "this is close to death", would all be meaningless. We can't predicate a purely mental category of something and then claim that the statement has a meaning outside our minds. Nor can we say our mental categories are approximations of anything real unless we categorize based on something that really exists in the first place.
I was going to write the same thing. Life, Death, Alive, Dead - these are all terms created by humans to make sense out of the world. In reality it's about more life-like and less life-like.
"Hume, with his criticism of the concept of causality, awakened him from his dogmatic slumbers--so at least he says, but the awakening was only temporary, and he soon invented a soporific which enabled him to sleep again."