How is "life" objectively defined?

  • 1
    'Objective' is a hollow, meaningless addition in the question. Yes, there are philosophies with a clear-cut difference. Most of them come with some phenomenological difference like specialised parts working in unison to sustain and expand the processes within a certain gestalt and the gestalt itself. Others are different. But the whole "prove" and "objective" part does nothing but obscure the question and makes it more about opinion and discussion.
    – Philip Klöcking
    Apr 13, 2022 at 6:21

4 Answers 4


There is a scientific border between life and non-life as you say. From a historical point of view we first separated things to organics and non-organics up until 1828 that a scientist, Wohler, made an organic compound called urea from some inorganic compounds. And today we know that all organic compounds are made up of inorganic ones. But your question is a bit harder to answer because the definition of life is not that obvious. If life means living organic things then there is still a way to separate a live organic stuff from a dead one by their physical/thermodynamical state.

From the simplest organic compound, urea, to the most sophisticated organ on the planet earth, human brain, there are different borders that can also be considered as the border between life and non-life, for example some biologists believe that viruses are the smallest living things because they can reproduce and conserve their RNA, most others believe that biological cells like bacteria are the first living things due to the reproduction of the whole cell using their DNA. There are also other borders, for example living things are energy/mass consuming they must be constantly fed. What ever you chose to be the border you'll find out that it's not something special and you could have chosen another border. It's not an objective border, it's just a definitive border.

  • 1
    Precisely, there's no boundary, otherwise, the answer would be simple. Another opinion.
    – RodolfoAP
    Apr 13, 2022 at 5:58

There are a host of potential criteria which have been suggested and the potential exceptions to each putative criteria make this a somewhat difficult question to answer unambiguously. Nevertheless the most plausible candidates are

  1. Living things do or have the potential to undergo the process of darwinian evolution
  2. Living Things are information processing 'machines' (if you will) whose causal capacities and downstream behavior are dependent both on stored prior information (DNA) and to the experiences manifest in their respective lives
  3. Living things are uniquely intentional homogeneous forms of matter which have the capacity for (some form of) representation, by which novel causal (possibilities) are made actual.

Though there are many others, the most plausible involve information retaining and modifying capacity, which imply the possibility of alternative histories depending on the set of actualities which occur. These are dependent on the information processing mechanisms made possible by the existence and function of DNA and correlated gene expression, which are causally necessitated by the organism being involved in evolutionary processes.

  • I like "life is what evolves" as a strong mapping to the common language intent - although I'd suggest "life is a material process that evolves", to exclude e.g. codes of laws, chess-learning computer programs.
    – g s
    Apr 23, 2022 at 1:25

When I was at school, which was a long time ago and so things may have changed somewhat, we were taught that living organisms exhibit a number of properties:

  • they move
  • they reproduce
  • They make new cytoplasm
  • They respire
  • They respond to stimuli And probably one or two others. This still more or less holds up since self-replicating machines are still rather limited. However, this definition tells us how to identify a living organism rather than telling us what life is. It would be fair to say that life is a property of living organisms rather than a thing in itself and so you could argue that it doesn’t exist depending on your definition of ‘exist’. By such a definition you would probably also say that other properties such as size, weight and time don’t exist, which seems counterintuitive to me but of course a word can mean anything that we agree it means.
  • I think this depends on one's view of whether there are natural kinds, and if so whether "life" is one--if something is a natural kind, we may say that a definition that picks out all members of that kind and nothing else is more "natural" than other definitions that don't correspond to natural kinds. I think few modern scientists would consider "life" to be a natural kind in the metaphysical sense of a category with 100% objective boundaries, though--that's what I interpret the point of the Scientific American article to be.
    – Hypnosifl
    Mar 13, 2022 at 21:24
  • All such features can be observed in a rock: it moves and changes shape very slowly, can break in two, and the parts grow due to accumulation of minerals -reproduction-, can produce equivalents to cytoplasm very slowly (cytoplasm already implies life, which is a fallacy: citoplasm defines life and not the opposite), can "respire" producing chemical reactions in the air, very slowly, and oppose an action with a reaction, or producing chemicals if subject to pressure, both of which are answers to stimuli. That view of life is very old.
    – RodolfoAP
    Apr 13, 2022 at 6:06
  • @RodolfoAP I’m inclined to agree on the whole. I disagree though with your assertion that cytoplasm defines life. If you would like to our forward a different definition of life then I’d be interested to hear it.
    – Frog
    Apr 13, 2022 at 19:51

Life tries.

Nonliving chemical processes don't try anything. When they run out of resources, they simply stop.

Living beings try to keep on living. They do whatever they can to keep on going:

  • They try actions to collect more resources (energy and building blocks)
  • They try to use the resources to maintain and improve their own ability to collect and use resources
  • They try to multiply to keep the species alive despite the eventual death of the individual.

Here is Dr Jeremy Sherman describing the difference between living and dead:


  • I can say that a teddy bear tries to keep its integrity (proved that it does not break easily), so, according to this definition, the teddy bear is alive. Evidently, "life tries" is not measurable, not formal, not science from any perspective, and it is mostly a subjective interpretation. Teddy bears are alive because they try, for a huge number of people (kids), so, they must be alive...?
    – RodolfoAP
    Apr 13, 2022 at 6:12
  • 1
    A protozoon does not try anything either. It just does. The very notion of trying implies the representation of a state different from what is. This, in turn, certainly is not the case for anything that does not have a brain, even according to the more liberal philosophies when it comes to consciousness in animals. Prime example of anthropomorphic fallacy imho.
    – Philip Klöcking
    Apr 13, 2022 at 6:34
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    As stated, this is an illegitimate projection of our notion of how things can/should be onto something that does not exist in these categories. The pragmatic context of trying vs. doing, as a notion and symbolic representation of a state, is exactly that trying describes the conscious effort to achieve a certain state. Plants do not literally try to grow towards the light, the chemical reactions in their structures are so that if sunlight hits one side of the stem more than the other, the growth there is locally inhibited more and thus there is an automatic alignment towards the light.
    – Philip Klöcking
    Apr 13, 2022 at 8:18
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    They just do follow their genetic programming in interaction with their environment. All the time. The first level of life where you can question that is where there is a complete, central neuronal representation of the body in its environment. Philosophy is sceptical of uncritically applying the notion of purpose on nature since at least Kant, since it implies someone who conceived and installed things according to purpose, ie. implies agency of or behind nature itself. While there are fringe positions holding that, this is certainly screaming for citations and justifications.
    – Philip Klöcking
    Apr 13, 2022 at 8:45
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    Counter question: How does "living things survive (live) and dead things don't" tell us anything about how to differentiate the two? It is completely circular, a tautology. A protozoon and a stone both behave to their environment according to their inner laws, following perfectly determinable causal laws. There is no verifiable or phenomenologically significant difference to be made in what you suggest there. So at the moment where you say 'look, the protozoon tries to survive' you can do so only according to other criteria or you presupposed what is to be determined, ie. that it is life.
    – Philip Klöcking
    Apr 14, 2022 at 9:52

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