Many Indian Scriptures such as Shiv Swarodaya describes the order in which elements comes in existence.
“Aakasha” – Space is considered to be the first and highest, most subtle element.
From Space, Air is supposed to be born.
Fire is said to be born from Air
Water is born as Fire cools down, and
Water is supposed to give birth to Earth.
So the hierarchy from most subtle to most gross is defined as Space, Air, Fire, Water and Earth.
When we look closely the Astrological signs which belong to a particular element, we can clearly find the order of philosophical to physical, subtle to gross, intangible to tangible properties follows the same order.
Air signs comes first and always considered as a philosophical signs more concerned with mental energies and high level planning than physical execution. Air is also intangible, all we can do is feel it but no touching or holding in hands.
Fire signs comes second and they are considered to be related to “Dharma” or our daily way of life. Fire is also subtle but more tangible than air, we can see fire, feel it and even touch but obviously not hold.
Water signs comes next and are related to emotional and relationship matters. Water indeed is more tangible as we can touch, feel and even hold with some effort.
Earth signs are comes last and are mostly related with physical, gross matters.