Tennessen finds empirical scientific facts and associated world views insupportable. He points out that scientific facts are based upon human perceptions which are variable from time to time depending upon attitude and motivation. He argues that interspecies differences in structure and behavior are so great as to suggest different perceptions and world views. Tennessen also asserts that the value of "world views' themselves must be very limited and indecisive in choosing between data or eliminating the inconsistencies in data, because the conceptual frameworks of science are evoked by the empirical facts which they include.