Could Impressionism have existed without the work of Edouard Manet?
A pioneer of an art that was distinctively nineteenth-century, Edouard Manet was avant-garde, as he depicted the contemporary life of the city, the boulevards, and the boudoir. Of course, his works caused scandal; so, his contemporaries were fairly certain that he was the leader of a new school, whether it was called "Impressionist," "Intransigent," or "Realist."
Manet struck out in a different direction as a painter of contemporary scenes, a subject that the Impressionists imitated, but they went in plein-air [outdoors].
He represented a middle ground between the academic side of French art, with its often-rigid adherence to tradition, and the experimental, individualistic tendencies of artists such as Honoré Daumier and Gustave Courbet
In the spring of 1863, Manet showed paintings at a small gallery on the Boulevard des Italiens. One painting, Music in the Tuileries was rejected as "trivial."
Two of Monet's paintings caused scandal: Dejeuner sur l'Herbe (1863) and Olympia (1863). These paintings of nudes that looked back at the viewer in less than nymph-like glances, led to Manet's reputation as the chief of the rebellious moderns. At some point in the later 1860s, these modern painters began to gather around him in the evenings. Later, they became known as the Impressionists. They were Degas, Monet, Renoir, Pissarro, Sisley, Bazille, and Cezanne, known as la bande de Manet. However, Degas detested the label "Impressionist" and became the 'odd man out' among the Impressionists.
Source: Mannering, Douglas, ed., Masterworks Impressionists. Bristol, England: Sweetwater Press, 1997.