Please think of just a handful of atoms of the elements carbon, hydrogen, nitrogen, and oxygen, and all the many ways to combine them with each other; it is surprisingly many possibilities already. Adding only a few more atoms, creates MANY more possibilities. Even for quite a few atoms of C, H, N, and O, the theoretically possible chemical space offers an enormous number of combinations. Therefore, categorization of compounds is a must, unfortunately. Probably the best way of giving you a feeling of what is possible here is via calculating the maximum possible number of combinations, the “chemical space”. This is attempted via the calculation on napkin III. Possibilities explode when the elements sulfur and phosphorus are added. Collectively, these six elements are called the CHNOPS elements; they make up the vast majority of living matter.