In retrospect, the definition of chemistry seems to invariably change per decade, as new discoveries and theories add to the functionality of the science. Shown below are some of the standard definitions used by various noted chemists:

* Alchemy (330) – the study of the composition of waters, movement, growth, embodying, disembodying, drawing the spirits from bodies and bonding the spirits within bodies (Zosimos).[25]
* Chymistry (1661) – the subject of the material principles of mixt bodies (Boyle).[26]
* Chymistry (1663) – a scientific art, by which one learns to dissolve bodies, and draw from them the different substances on their composition, and how to unite them again, and exalt them to a higher perfection (Glaser).[27]
* Chemistry (1730) – the art of resolving mixt, compound, or aggregate bodies into their principles; and of composing such bodies from those principles (Stahl).[28]
* Chemistry (1837) – the science concerned with the laws and effects of molecular forces (Dumas).[29]
* Chemistry (1947) – the science of substances: their structure, their properties, and the reactions that change them into other substances (Pauling).[30]
* Chemistry (1998) – the study of matter and the changes it undergoes (Chang).