Critical thinking is thinking that questions assumptions. It is a way of deciding whether a claim is always true, sometimes true, partly true, or false.
Critical thinking is a rich concept that has been developing throughout the past 2500 years. The term "critical thinking" has its roots in the mid-late 20th century. It can be traced in Western thought to the Socratic method of Ancient Greece and in the East, to the Buddhist kalama sutta and Abhidharma.