The 18th edition emphasizes that while (etiquette) may change, the principles (manners) do not. Respect: Treating others as if they are valuable.
Failing to respond to an invitation is still considered a major breach of social contract. The Bottom Line Emily Post's Etiquette, 18th Edition
Etiquette often gets a bad rap as a list of rigid "don’ts" and dusty traditions. However, the 18th Edition of Emily Post’s Etiquette: Manners for a New World reminds us that at its core, etiquette is about one thing: The 18th edition emphasizes that while (etiquette) may