"The ability to tell almost instinctively who painted a picture is defined ... as connoisseurship". Connoisseurs evaluate works of art on the basis of their experience of the style and technique of artists. Judgment informed by intuition is essential, but it must be grounded in a thorough understanding of the work itself. On the basis of empirical evidence, refinement of perception about and form, and a disciplined method of analysis, the responsibility of the connoisseur is to attribute authorship, validate authenticity and appraise quality. These findings are crucial for the valuation of works, and can be collected and organized into a "catalogue raisonné" of the work of a single artist or a school.