\begin{definition}[Definition:Natural Place]
According to the ancient Greek philosophers, everything had a position in the universe where it was most comfortable.
That position was referred to as its '''natural place'''.
Hence, when displaced from its '''natural place''', it would eagerly try to return to that '''natural place'''.
Hence:
:a stone, being made of earth, when released from a hand holding it in midair, will push downwards in order to return as soon as possible to the centre of the universe, that is, Earth.
:tongues of fire will shoot upwards, so as to rise to its '''natural place''' above the sphere of air
:bubbles of air will rise up through water to its '''natural place''' above the sphere of water.
\end{definition}