set forth in his Systema Naturae (1735) and subsequent works. A major discussion in the scientific literature is whether a system that was constructed before Charles Darwin's theory of evolution can still be fruitful and reflect the development of life. Astronomy's Three Kingdom System Is a classification of celestial objects suggested by Steven J. Dick (2013 and 2019). This system classify all celestial objects in 82 classes of objects. The top categories are the three kingdoms: "Kingdom of the Planets", "Kingdom of the Stars" and "Kingdom of the Galaxies". Each kingdom is divided to a number of families and subfamilies and further subdivided to the 82 classes. Astronomy is a fine example on how Kuhn's (1962) theory of scientific revolutions (or paradigm shifts) influences classification. For example: Paradigm one: Ptolemaic astronomers might learn the concepts “star” and “planet” by having the Sun, the Moon, and Mars pointed out as instances of the concept “planet” and some fixed stars as instances of the concept “star.” Paradigm two: Copernicans might learn the concepts “star,” “planet,” and “satellites” by having Mars and Jupiter pointed out as instances of the concept “planet,” the Moon as an instance of the concept “satellite,” and the Sun and some fixed stars as instances of the concept “star.” Thus, the concepts “star,” “planet,” and “satellite” got a new meaning and astronomy got a new classification of celestial bodies. Hornbostel-Sachs Classification of Musical Instruments Is a system of musical instrument classification devised by Erich Moritz von Hornbostel and Curt Sachs, and first published in 1914. In the original classification, the top categories are: Idiophones: instruments that rely on the body of the instrument to create and resonate sound. Membranophones: instruments that have a membrane that is stretched over a structure, often wood or metal, and struck or rubbed to produce a sound. The subcategories are largely determined by the shape of the structure that the membrane is stretched over. Chordophone: Instruments that use vibrating strings, which are most commonly stretched across a metal or wooden structure, to create sound. Aerophones Instruments that require air passing through, or across, them to create sound. Most commonly constructed of wood or metal. A fifth top category, Electrophones: Instruments that require electricity to be amplified and heard. This group was added by Sachs in 1940. Each top category is subdivided and Hornbostel-Sachs is a very comprehensive classification of musical instruments with wide applications.