To me, there seems to be a pretty straightforward line to draw between life and non-life: Life is that which undergoes Darwinian evolution.
If (a) it makes copies of itself, (b) the copies inherit traits from the original, (c) the traits are subject to variation/mutation, and (d) the success of the copies at making further copies depends on those traits which are inherited, then evolution must occur.
Every other definition seems to me over-complex and ad-hoc; like specific things we have noticed which tend to be true about most life on Earth, but which might not be true for special cases, or for some other hypothetical extraterrestrial life which we might discover someday.
This definition is an unambiguous binary classifier, and it seems to correctly categorize everything we would intuitively call "alive". (Also, under this definition, viruses are unambiguously life).
If (a) it makes copies of itself, (b) the copies inherit traits from the original, (c) the traits are subject to variation/mutation, and (d) the success of the copies at making further copies depends on those traits which are inherited, then evolution must occur.
Every other definition seems to me over-complex and ad-hoc; like specific things we have noticed which tend to be true about most life on Earth, but which might not be true for special cases, or for some other hypothetical extraterrestrial life which we might discover someday.
This definition is an unambiguous binary classifier, and it seems to correctly categorize everything we would intuitively call "alive". (Also, under this definition, viruses are unambiguously life).