Here are 10 philosophical ideas that everyone should understand:

1. The nature of reality. What is reality? Is it something that exists independently of our minds, or is it a product of our own minds? This is one of the most fundamental questions in philosophy, and there is no easy answer.
2. The nature of knowledge. How do we know what we know? Is knowledge based on reason, experience, or something else? This is another fundamental question in philosophy, and there are many different answers.
3. The nature of morality. What is right and wrong? What is the basis for morality? These are questions that have been debated by philosophers for centuries.
4. The nature of freedom. Do we have free will? Or are our actions determined by our genes, our environment, or something else? This is a question that has important implications for our understanding of ourselves and our place in the world.
5. The nature of consciousness. What is consciousness? How does it arise? These are questions that have puzzled philosophers for centuries.
6. The nature of beauty. What is beauty? Why do we find certain things beautiful? These are questions that have been explored by philosophers, artists, and poets for centuries.
7. The nature of justice. What is justice? How should we distribute resources and opportunities in society? These are questions that have been debated by philosophers and politicians for centuries.
8. The nature of love. What is love? How does it work? These are questions that have been explored by poets, philosophers, and psychologists for centuries.
9. The meaning of life. What is the meaning of life? Why are we here? These are questions that have been pondered by philosophers and theologians for centuries.
10. The nature of death. What happens after death? Is there an afterlife? These are questions that have been asked by people for as long as there have been people.

These are just a few of the many philosophical ideas that everyone should understand. Philosophy can help us to think more clearly about the world around us, and to make better decisions about our lives.