Complex sentence: Mercier nevertheless received a decent education and began his literary career by writing heroic epistles, but early came to the conclusion that Boileau and Racine had ruined the French language, and that the true poet was he who wrote in prose.
Split into simpler sentences: Mercier nevertheless received a decent education and began his literary career by writing heroic epistles. He early came to the conclusion that Boileau and Racine had ruined the French language, and that the true poet was he who wrote in prose.