The definition of life is based on what we observe, on empirical observations, which is the best kind of knowledge. The current definition may not be perfect, b

The definition of life is based on what we observe, on empirical observations, which is the best kind of knowledge. The current definition may not be perfect, but it's useful enough to predict phenomena, such as how life on other planets might look like. And this is the opposite of arbitrary. You're getting into metaphysics, which is in general not useful. I mean, Nietzsche's essay on words being lies is entertaining and all, but ultimately just something to contemplate when stoned.