Complex sentence: Isabella Thorpe gives Catherine a list of seven books that are commonly referred to as the'Northanger horrid novels'; these works were initially thought to be of Austen's own invention until the British writers Montague Summers and Michael Sadleir found that they actually did exist.
Split into simpler sentences: Isabella Thorpe gives Catherine a list of seven books that are commonly referred to as the'Northanger horrid novels'. These works were initially thought to be of Austen's own invention until the British writers Montague Summers and Michael Sadleir found that they actually did exist.