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Linné on line arrow Physics and the Cosmos arrow Physics and the Cosmos arrow The world according to the ancient Greek philosophers

The world according to the ancient Greek philosophers

The four elements

Matter consists of four different elements, namely water, air, fire and earth. This was claimed by the Greek philosopher Empedokles from Akragas in the 5th century BC. He called the elements the roots of the matter and it was only after Aristotle (388-322 BC) that they were called elements. The elements were considered as eternal and invariable and they could not be explained.  

According to Empedokles there were also two active principles that united and divided the elements, love and discord. Whereas love was the uniting principle which kept the elements together in different substances, discord was the principle which divided the elements. At this time one did not think that empty space could exist. Therefore love and discord were also counted as elements which filled the void between the others.


Tetrahedron

Hexahedron

Octahedron

Icosahedron

Later, Plato linked the four elements with different geometrical bodies, called Plato's bodies. Fire was represented by the tetrahedron, earth by the hexahedron (cube), air by the octahedron and water by the icosahedron.

The atomic theory

According to the atomic theory of the Greeks everything consists of indivisible atoms (atom means indivisible in Greek). The atomic theory, which was one of the precursors of the theory of four elements, was introduced by Leukippos around 440 BC but is mostly connected to his pupil Democritus who developed it further. Aristotle and others opposed the atomic theory. Instead they maintained that matter is infinitely divisible.

Apart from being indivisible the atoms are also rigid and solid. On the other hand they are not all equal in shape, only in their composition. The atoms move in empty space which therefore has to exist. The reason that individual atoms cannot be seen is that they are too small.

The atomic theory also made it possible to explain changes in the form of regrouping of the atoms. On the other hand the atoms themselves cannot be explained. This way of explaining things is still used in physics. We can explain one level by introducing a sub-level which we take for granted. For example we can understand the properties of the different elements in the periodic system by describing what we now call atoms as consisting of an atomic nucleus surrounded by a cloud of electrons. The atomic nucleus in turn can be understood in terms of protons and neutrons etc.