This paper examines non-default/default case environments in English and explores the nature of default case and its realization mechanism in this language. We advance four claims about the default case licensing mechanism: (ⅰ) The default case mechanism is capitalized on to spell out nominal expressions whose Case feature fails to be valued because of the deficiency of the Case value-licensing head, (ⅱ) Nominal expressions without Case valuation have case form through default case licensing at the morphological/phonological component, (ⅲ) Both Nominative and Accusative case can be default case in English, (ⅳ) The selection of the particular Case value through the default case mechanism depends on several factors such as relative positions of nominal expressions and the invariant strong form constraint (Quinn 2002).