Gilbert Munch said:
They've recently proved that actually Aristotle was right... kind of - he had the states of matter. The scientists' thoughts were this: solid = earth, liquid = water, gas = air, and plasma = fire. So, looking at it, scientifically all that exists is accounted for, so there is no 5th element.
Actually, that is still incorrect. The classic states of matter are, of course;
Solid
Liquid
and Gas.
Plasma isn't generally considered one of the classic states, but is a state of matter. However, we still have quite a few others to consider;
Liquid crystal states
Amorphous solid
Magnetically-ordered states
Superconductors
Superfluids
Bose-Einstein condensates
Rydberg molecules
and Quark-gluon plasma.
As well as a few more currently proposed states;
Degenerate matter
Supersolid
String-net liquid
and Superglass.
This suggests to me that there may be even more. So he may have been on the right track, but he missed a couple.
Also, normal natural fire generally isn't hot enough to create a plasma. While 'flames' can be present in the creation of a plasma, in Aristotle's time it seems unlikely that this is what he was talking about. (Thank you, Wikipedia) So the four 'elements' really don't describe the constituent parts of anything, nor do they really describe with any accuracy the states of matter.
However! If we're speaking strictly in mystical terms, as the OP seems so insistent on - I would like to agree with some other posters that the fifth element would be 'life' (Which is what I choose to believe the movie was trying to say anyway). None of the other elements really account for growth, animation, or anything like thought. 'Death', if you wanna throw it out there too, is just the absence of life, and therefor not an element.
