There are hundreds of psychotherapy approaches or schools of thought. By 1980 there were more than 250; by 1996 more than 450; and at the start of the 21st century there were over a thousand different named psychotherapies—some being minor variations while others are based on very different conceptions of psychology, ethics (how to live) or technique. In practice therapy is often not of one pure type but draws from a number of perspectives and schools—known as an integrative or eclectic approach. The importance of the therapeutic relationship, also known as therapeutic alliance, between client and therapist is often regarded as crucial to psychotherapy. Common factors theory addresses this and other core aspects thought to be responsible for effective psychotherapy.