to ground something, such as one's opinion, decision, or thinking, on someone or something; to found one's ideas or attitude on something. (Upon is more formal and less commonly used than on.)I base my opinion on many, many facts.I based my opinion upon my own seasoned judgment.
To form, develop, or found something on the basis of something else: I based my decision on the information you gave me. The film was based on a popular book.