Opus number developed other catalogue-number systems; among them the "Bach-Werke-Verzeichnis" (BWV-number), and the "Köchel-Verzeichnis" (K- and KV -numbers) with which are organised the works of Johann Sebastian Bach and Wolfgang Amadeus Mozart, respectively. In the classical period, the Latin word "opus" ("work", "labour") was used to identify, list, and catalogue a work of art. By the 15th and 16th centuries, the word "opus" was used by Italian composers to denote a specific musical composition, and by German composers for collections of music. In compositional practise, numbering musical works in chronological order dates from 17th century Italy, especially Venice. In common usage, the
19th-century philosophy physical and empirical and is only realized through the individual's intuition, rather than through the doctrines of established religions. "Social Darwinism" refers to theories that apply the evolutionary concept of natural selection to human society. 19th-century philosophy In the 19th century, the philosophies of the Enlightenment began to have a dramatic effect, the landmark works of philosophers such as Immanuel Kant and Jean-Jacques Rousseau influencing new generations of thinkers. In the late 18th century a movement known as Romanticism began; it validated strong emotion as an authentic not of aesthetic experience, placing new emphasis on such emotions as trepidation, horror