The term Baroque probably derived from the Italian word barocco, which philosophers used during the Middle Ages to describe an obstacle in schematic logic. Subsequently, the word came to denote any contorted idea or involute process of thought. Another possible source is the Portuguese word barroco (Spanish barrueco), used to describe an imperfectly shaped pearl. In art criticism the word Baroque has come to describe anything irregular, bizarre, or otherwise departing from rules and proportions established during the Renaissance. Until the late 19th century the term always carried the implication of odd, exaggerated, and overdecorated. It was only with Heinrich Wölfflin’s pioneering study, Renaissance und Barock (1888), that the term was used as a stylistic designation rather than as a term of thinly veiled abuse and that a systematic formulation of the characteristics of Baroque style was achieved.