Plato’s major contribution to philosophy was his metaphysical theory of forms. Plato’s forms were divine objects, known by the mind through thought. The practice of such thought was believed to provide the best life. The forms, like the primary substance of the Pre-Socratics, were responsible for all of the things experienced by human beings and for the very existence and qualities of human beings, animals, natural objects, and man-made objects. Indeed, the entire world of existence was held to be made up of copies of the forms. Even ideas, such as beauty, truth, and justice, had forms. Although to Plato it was viewing the mind’s representations of the forms, not the actual forms themselves, that mattered. The forms were unchanging, perfect, and divine. Everything that humans could think, perceive, or imagine, and the existing objects of thoughts and perceptions, were but imperfect copies of the forms.