I agree. I think a source of confusion is the following.

Everyone has built up, over their lifetime, an implicit mental notion of "life", which is based upon the sorts of characteristics of things they classify as being alive. Many (I'd say most) people think this mental notion is some objective category that exists external to their mind, some thing that has a kind of essence that is shared by all the instances of life. They see the task of defining life as defining the essence of this category, and see there being an objective question as to whether something (e.g. a kind of virus) fits this category.

But this is to confuse a mental construct with what is out there. There are the objective properties of things like different types of viruses, different types of bacteria, of different types of mammals, and of all other natural phenomena. You can talk about what the similarities and differences are between the objective properties of a type of virus and a type of bacteria, for example, and there are simpler kinds of phenomena vs more complex ones, but there's no actual "life" category out there, separate from our mental constructs, to be objectively defined.

would it be safer to say everything in on spectrum between alive and not alive?

Even chemicals "evolve"

http://www.dictionary.com/browse/chemical-evolution

Thats "The Categories Were Made For Man, Not Man For The Categories".

Sb trying to push sb else to use a definition meets the second part of the sentence.

>Sb trying to push sb else to use a definition meets the second part of the sentence.

This is post-modernism in thin disguise.

Certain categorizations can be more valuable (practical, useful, just, etc) than others, in which case it's reasonable to rally for their use over other, less valueable, categorizations.

I don't know about the post-modernism thingy.

To the second part: To one practical is to the other unpractical. To one just is to another unjust.

To push certain categories over others just says to me you want them to be in your frame(practical, useful for you I guess?).

And to not give an argument on the usefulness is to hide intention. But I'm not too firm on that yet.

Some categories are just completely impractical, for example the category of "all objects except for my dog and its kibble, and excluding those that came in to existence on an even-numbered Gregorian year." Language is an application of signaling theory and there are lots of statements we can make about it. (For example it would be a bad idea to re-define the word "good" to mean that one above.)

It's post-modernism only if you assume that human beings have no set, general psychological characteristics and are entirely the product of socialization. Otherwise it is pragmatism.

Huh?

It's most assuredly post-modernist because it implicitly assumes that all categories are equal in value (i.e.: that no category is better than another), and that the decision is at it's core a power-struggle (i.e.: oppressive to the loser).

This is, again, a tired and fruitless approach.