Moving in space, the atoms originally were individual units, but inevitable they began to collide with each other, and in cases where their shapes were such as to permit them to interlock, they began to form clusters. Water, air, fire, and earth, these are simply different clusters of the changeless atoms.
DemocritusBy convention sweet is sweet, by convention bitter is bitter, by convention hot is hot, by convention cold is cold, by convention color is color. But in reality there are atoms and the void. That is, the objects of sense are supposed to be real and it is customary to regard them as such, but in truth they are not. Only the atoms and the void are real.
Democritus