Skepticism. – The method of practicing doubt when regarding what is held as knowledge.
Realism. – The belief that reality exists independently of our own observation or perception.
Idealism. – The philosophical view that asserts that reality is fundamentally based on, and shaped by, ideas and mental experience, rather than material forces.
Existentialism. – The idea that all philosophical thought must begin with the experiences of the individual, and it is up to the individual to give meaning and authenticity to their own experience.