The purpose of science is to discover the nature of reality concealed under surface appearance. Based on this definition, Marx makes the above assertion - if things appeared exactly as they are, there would be no need for science to remove the veil of appearance. Social science, therefore, is the search for the real nature of society, underneath all of its visible, external facades. If the reality of society is easily observable in our everyday experience, then there is no need for scientific reflection on society, as Marx defines science. The idea that society has an 'appearance', which is not the same as social 'essence', forms the starting point for the Marxist discussion of ideology. Ideology is what allows a society to persist, even though the essence of that society may contain contradictions.