Complex sentence: The eldest son of a Duke, Marquess or Earl almost always uses one of his father's subsidiary titles as a courtesy title; for instance, the eldest son of the Earl of Snowdon is called Viscount Linley.
Split into simpler sentences: The eldest son of a Duke, Marquess or Earl almost always uses one of his father's subsidiary titles as a courtesy title. For instance, the eldest son of the Earl of Snowdon is called Viscount Linley.