Critical thinking is a higly valued skill today not only in academic settings, especially in higher education, but also in professional enviroments. Employers expect individuals who think critically; teachers want students who think critically; society need citizens who think critically. Critical thinking integrated with business and economic success, necessary for democratic citizenship, and a vital part of professional pactice. Although critical thinking is seen important in all areas yet, there is no consensus on its definition. Especially when no consensus on its’ definition some assumptions are suggested that critical thinking can be learned and critical thinking improves the quality of professional practice. This article provides various definitions and assumptions based on views of pioneer scholars on critical thinking.