The number and identities of metalloids depend on what classification criteria are used. Emsley[41] recognised four metalloids (germanium, arsenic, antimony and tellurium); James et al.[42] listed twelve (Emsley's plus boron, carbon, silicon, selenium, bismuth, polonium, ununpentium and livermorium). On average, seven elements are included in such lists; individual classification arrangements tend to share common ground and vary in the ill-defined[43] margins.[n 5][n 6]