My definition, like ALL definitions, is arbitrary but that does not mean it (or others) are not designed to be useful.
Again, not all definitions are arbitrary. c, for example, is not arbitrary- there's nothing else like it. There's no fuzzy line possible there. Many concepts in mathematics and physics are non-arbitrary- the names we give them may be arbitrary (as language is), but the concepts themselves are not, and have clear meanings without any ambiguity. Likewise, in philosophy, there are many non-arbitrary concepts.
The arbitrary nature of your definition naturally invalidates it as far as any philosophical relevance goes (and you were trying to argue not against a scientific point, but against a more philosophical one- a moot point, but still).
ANY definition of 'life' is going to be arbitrary unless it is inclusive of the natural extremes and embodies a true conceptual whole- Grumpy's definition is much better, (I'm a little skeptical of the relevance of 'molecule'. I don't think life has to be molecular- but he achieves therein a full spectrum which encompasses all potential extremes rather than drawing subjective lines without justification).
I think the concept boils down to self replication of an information system from its environment.
Grumpy's definition being one of Molecular life (which I find acceptable for that qualification).
The most important characteristic of a well defined definition is that it clearly describes the object or field it is defining so that the borders are not vague.
Sure, but that doesn't make it philosophically useful. In order to be useful philosophically, it must also have the characteristic of not being arbitrary.
That is something Grumpy Achieved (if we assume his is limited to "molecular" life).
You not may the result that prions and currently "printed objects" can not be alive. If not, offer your alternative definition of life.
I'm not sure what you're saying. But Grumpy and I have both presented less arbitrary definitions.
To demonstrate the importance of the definition being solid and non arbitrary, I will give you this.
Following from your explanations of why Prions are not life:
"Thus when it happens to be a prion that hits the existing protein molecule to trigger the refolding making another prion, I don´t consider that refolded molecule to be life. It could have been created by non-piron collisions too - no "reproduction.""
The only conclusion, based on that, to be made is that life does not exist and can not exist. None of us are alive- because there are *possible* non-living mechanical means by which we could come into existence- and in fact, if we follow the chain back through generations, there are possible non-living mechanisms that must have originated our ancient ancestors (discounting time-travel).
Invalidating the life of a prion because it could have been formed by a non-living process invalidates the life of everything that could have been formed by non-living processes- including the first life forms, whatever they were, which must have been so formed- thus invalidating the life of everything that came after (having been formed by something non-living).
This may not be a problem with every day usage, but it's a gaping hole in your definition if you try to put it forwards in a philosophical context.