Shape and ornamentation are evidence that even in such a rigid and stylized form there is room for creativity and difference. Renown art historian Ernst Gombrich developed a theory to explain these changes and referred to it as schema and correction. If we were to look at one vase as the plan or schema, we can see how one artist might take this schema and update it in order to make the design more pleasing according to the artist's and clients' tastes. These changes are referred to as the correction.