The four-year, full-time undergraduate program comprises a minority of enrollments at the university and emphasizes instruction with an "arts and sciences focus". Between 1978 and 2008, entering students were required to complete a core curriculum of seven classes outside of their concentration. Since 2008, undergraduate students have been required to complete courses in eight General Education categories: Aesthetic and Interpretive Understanding, Culture and Belief, Empirical and Mathematical Reasoning, Ethical Reasoning, Science of Living Systems, Science of the Physical Universe, Societies of the World, and United States in the World. Harvard offers a comprehensive doctoral graduate program and there is a high level of coexistence between graduate and undergraduate degrees. The Carnegie Foundation for the Advancement of Teaching, The New York Times, and some students have criticized Harvard for its reliance on teaching fellows for some aspects of undergraduate education; they consider this to adversely affect the quality of education.