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I repeat, what is the difference between you who are alive and one who is dead? I know that you are intelligent enough to know the difference. It is just logical.
Well, I know this attempt at education will most likely be ignored, but I'll take a stab at this question, PeaceCrusader.
Some common characteristics of an organism that is alive (I assume you mean humans here, because of the use of the phrase "you who are alive):
1) Is contiguous and maintains homeostasis. It's hard to imagine an alive human who can't maintain a physical boundary to their body and has no control whatsoever over their temperature, pH level, oxygen saturation, etc.
2) Has a metabolism - needs to intake nutrients (or "burn" stored molecules) and produces useful energy for work.
3) Has at least the theoretical ability to reproduce, even though it may not be used in practice or may no longer be functional / may be damaged.
4) Can regrow certain cells / bodily structures and can recover from injury.
5) Can respond to stimuli within the range of human perception.
Not every human meets all 5 of the above, but I'd venture to guess that if you can't meet *any* of the 5, you're pretty much dead. That's my stab at it.
Let me guess - your explanation has something to do with having / not having a spirit / soul, right? While I personally believe that such ethereal constructs exist, the scientist in me can't doesn't allow that personal belief to enter the realm of science. Which is where the definition of "dead or not dead" firmly lies.
We could get into some interesting side-threads regarding fables of homunculi / golems / revenants / similar creatures that are alive but have no spirit / soul or dead but have a spirit / soul but I don't see anything productive coming out of that, because there's no scientific proof of a spirit / soul in the first place.