Comment by griffzhowl

Life is very useful as a term because it allows you to define a 'not living' term as well: dead. And it has meaning at the highest level. But if you start looking at things in a more detailed way even death doesn't arrive 'all at once' for multi cellular organisms, for instance a dead person's hair still grows to the point that corpses need to be shaved. And a virus may be dead by one persons view on what 'life' is all about but alive by someone else's definition. And depending on the context both of them may be right.

The definition is fuzzy because the concept is fuzzy! Even something that we in every day life see as settled such as a species is not always clear-cut. Cat or dog? That's usually easy. Member of a species yes or no? Not so easy, and in some cases subject to considerable debate and even then unresolved.

For instance:

https://en.wikipedia.org/wiki/Species_complex

And:

https://en.wikipedia.org/wiki/Ring_species

Boundaries are hard, just like naming things.

We really only have one example of life (or at least all our examples are interconnected), so I don't expect great definitions.

Just like geology doesn't have a great definition for their subject of study (the earth). They have a definition that works really well, but because they only have one example, the definition ain't stress tested.

Slightly less silly: it took the discovery of lots more bodies inside and outside the solar system (dwarf planets here, exoplanets elsewhere) for astronomers to really nail down the definition of planet.

I find Maturana’s definition satisfactory. Best overview in his book with Francesco Valera:

Autopoiesis and Cognition: The Realization of the Living (1980)

https://en.wikipedia.org/wiki/Autopoiesis_and_Cognition:_The...

Unfortunately out of print.

I think that depends on your prior expectations about how biological concepts should be structured. I was trying to make the case that we should expect that they're fuzzy when we're dealing with very complex phenomena that exhibit a lot of variation. The fact that these kinds of phenomena happen to exhibit clustering is what makes (fuzzy) classification possible, but we also find that many phenomena or organisms are in borderland areas between clusters, so the classification doesn't work as well with them.

The problem is that it's really hard to come up with a definition that includes all of the things we agree are obviously life (e.g. mold), does not include fire, and does not just appeal to the particular structure that most or all life on earth seems to have (the cell).

The result is a landscape of fuzzy definitions mostly centered around that last one.

We only have a single tree-of-life (or possibly, several syncretic trees-of-life from a single planet) as an example. Makes it a little difficult to discern the true principles.

Analyze a word you think has a crystal clear definition.

Yeah, I think that's an interesting feature of linguistic thought: it builds on and exists within our deep evolutionary heritage of percetion and fuzzy classifications, but by the nature of words as being discrete items it also predisposes us to think naively that the phenomena referred to by words are also discretely organized into this box-like either/or structure, but the reality is more complex

Because in most cases the categories are invented by us, to make sense of the world. But the penomena themselves are often continuous. Or actually not just us but most life with some kind of sensory system - even paramecium differentiates between food and non-food.

Take our color perception as an obvious example: We clearly see different types of color, despite us being unsure at the thresholds in between, and the actual electromagnetic radiation of visible light being a continuous wavelength range.

That is just a fundamental limit of our reasoning. We mentally make models of the world to make sense of it. These models have to be of less complexity than reality, ergo they have to cluster perceptions, ergo we have to categorize.

I'd argue that this is FAR more true of the soft sciences - of which biology is perhaps the "hardest".

The definition of steel is pretty hard-edged. A polymer of C, H, and O isn't steel.

The definition of a quasar is similar. There are "maybe quasars", but that's from lack of data, not lack of definition clarity.

A circle is pretty exactingly defined. Mathematicians aren't fuzzy on that.