Passage: In chemistry, isomers are ions or molecules with identical formulas but distinct structures. Isomers do not necessarily share similar properties. Two main forms of isomerism are structural isomerism (or constitutional isomerism) and stereoisomerism (or spatial isomerism).

Question: What are the primary forms of isomerism known as?
structural isomerism (or constitutional isomerism) and stereoisomerism (or spatial isomerism)