I see the nature of monsters being more varied than the nature of monsters. For example, while animals act solely off instinct with very little deviation, the term monster in my mind infers it has [i]something[/i] beyond that. A monster might just be a malicious animal, one that knowingly acts with cruelty, but that is what sets it apart. A monster might also just be a beast or being with extraordinary capability beyond the accepted norm, but viewed rightfully or wrongly as frightening or fearsome.

A zoanthrope could be just as much a monster as it isn't. Just because it has the capacity to tear a man apart, and many chose to do so, does not mean they all are "monsters". Are they [i]monstrous[/i]? That I would agree on by virtue of their ability, regardless if they can exercise it or not, but it again does not qualify the exceptions as monsters just by that standard.

I bring this back around by citing my example of exceptional ability beyond the norm. Would a dragon be any less a dragon if it were just a flying lizard that could breathe fire? Still very much a "dragon" even if it had nothing but animal intellect and instinct. Why? Because the qualities it expresses greatly surpass the accepted normalcy. Does that rightfully make it a monster in our example? No, not really, but the perception is different.

This goes even deeper still when we start talking about legitimately intelligent monsters; people. Regular people are perfectly able to "devolve" into monsters based upon our past, current or even future standards. Why? Because they again either give the perception of, or worse yet, carry out heinous, grievous, horrific or brutal acts. Things considered too bad for human or animal standards. They go above and beyond the expectations of regular disdainfulness.

This might be wrongly placed, even positive things could be considered "monstrous" because of the perception of the persons involved. To give an anecdote relating to roleplaying, as appropriate to our forums here, I once was playing a human character alongside others. What they did not know, in our roleplay barring the Game Master's knowledge present, was that my character was endowed with psychic powers, specifically those relating to psychometabolism and alteration. When we finally found ourselves in a bad spot otherwise beyond hope, I had my character carry them out.

Whereas most the people were just shocked, one person out of character was adamant that what happened was "evil" and "monstrous" and that my character was no longer a person. Granted this translated into their character's behavior as well, but just the thought in reality that I would do or enjoy such a thing, even in fiction, was "wrong". That the concept made the character and me, by virtue, something less than human.

Short of this, there is not much I can add to how I determine the differences. In truth, I almost explicitly play "monstrous" beings or those animalistic and savage.