Any understanding of the nature of matter starts with the classification of matter into similar groups. One way to group them is by solids, liquids, and gases; a more useful grouping here is by the makeup of the matter. Materials around us are classified as elements, compounds [local] and mixtures. [local]
The definition of element has changed throughout the centuries, several Greek philosophers of ancient times viewed matter as consisting of some combination of four "elements". They viewed earth, air, fire , and water as the primary pieces of matter of which everything was composed. Antoine Lavoisier gave a definition of element on which we base the modern definition of elements and compounds [local].
Compounds and elements by definition are 'pure substances.'
