‘Forms of the periodic table’ discusses some of the different periodic tables that have been published and asks whether there is an ‘optimal’ periodic table. Meaningful differences only occur when one changes the order of the elements. Examples include moving the positions of hydrogen and helium to better reflect their chemical properties, or the shifting of elements to form triads of similar behaviour. Whether an optimal periodic table exists depends ultimately on one’s philosophy. Realists believe that the repetition of chemical properties is an objective fact, and so strive for the most accurate depiction of it. Instrumentalists believe that such depictions are simply a human construct and not ultimately important.