The term neoclassicism can be broken down into two parts: "Neo" and "Classic." This refers to the fact that is a new ("neo") interpretation of classic architectural and artistic concepts pioneered by the ancient Greeks and Romans. Art Deco and Art Nouveau are movements firmly planted in the twentieth century, and Mannerism and the Renaissance are much too far in the past to even be considered for a question that is about an eighteenth-through-twenty-first-century artistic movement.

Joseph Wright of Derby painted A Philosopher Giving a Lecture on the Orrery. It was painted between 1763 and 1765 CE. He was later considered the unofficial artist of the Enlightenment as a result of his paintings that largely had to do with scientific topics.

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Goya created these etchings as a series of criticisms leveled at the frivolity of Spanish society at the time. This fits with Goya's other work, in which social commentary was a frequent presence. Rembrandt and Velasquez were 17th century painters, while Tiepolo and Guardi were not quite contemporaries of Goya, both being from a previous generation and dying before these etchings were made.

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Los Caprichos is Goya's series created from 1797-1798, and it is notable for its recurring portraits of asses, bats, and other figures. The Disasters of War is a later series of etchings Goya made between 1810 and 1820 as a war protest. The Sleep of Reason... is perhaps the most famous etching from Los Caprichos, and Witches' Sabbath and The Madhouse are unrelated Goya works.

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This image is recognizably Rembrandt. Rembrandt is famous for portraits and self-portraits with stark lighting on the subject's face and a dark background behind. In addition, he often had his subjects pose in elaborate costumes like this, which depicts an old man in a turban.

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Jacques-Louis David was the foremost Neoclassical painter of late eighteenth century France, who was especially well known for his history paintings, such as The Oath of the Horatii shown here. Neoclassicism was a response to the excesses and embellishments of Rococo art, finding a clarity and precision in adopting classical themes from Ancient Greece and Rome. The Oath of the Horatii is based on a story from the Roman author Livy, and David presents the work in a highly composed format which reflects on the theme of loyalty to country and family.

Artwork from Wikimedia Commons: https://commons.wikimedia.org/wiki/File:Jacques-Louis_David,_Le_Serment_des_Horaces.jpg