SOMETHING THAT WAS MENTIONED BEFORE

• Jill: I've brought some books
• Rick: Put the books over there

WHEN THERE IS ONLY ONE OF SOMETHING

• The sun is hot today
• The Queen is coming

SOMETHING THAT BOTH SPEAKER AND LISTENER KNOW ABOUT

• The book you told me about was really interesting

WITH SUPERLATIVES

• I am the greatest

REFERRING TO GROUPS OF PEOPLE

• One law for the rich and another for the poor
• The English can be noisy at football matches

NAMES OF OCEANS, SEAS, RIVERS, MOUNTAIN RANGES (not mountains)

• the Atlantic [ocean] separates America from Europe
• the Mediterranean [sea] is in the heart of Europe
• the Thames flows through London
• I'm going skiing in the Alps

NAMES OF SOME COUNTRIES AND GROUPS OF ISLANDS

• the United States and the United Kingdom use the definite article
• the Canaries are a part of Spain